Grownup vs. Grown up – Which is Correct?

The choice between grownup and grown up depends entirely on the grammatical role and meaning you intend. Grownup (one word) is typically a noun referring to an adult, or sometimes an adjective. Grown up (two words) functions as a verb phrase (the past participle of “grow up”) or a phrasal adjective describing someone who has matured.

Grownup or Grown Up – Which is Correct?

Both “grownup” and “grown up” are grammatically correct in American English, but they serve different functions. The key distinction lies in whether you are using a single, compound word as a noun or adjective, or a two-word phrase acting as a verb or adjective. Misusing them often stems from confusion about their respective parts of speech.

The Best Trick to Remember the Difference

To remember the difference, think of “grownup” as a single, solidified concept—a person who is an adult. If you can replace it with “adult” (as a noun or adjective), then “grownup” (one word) is likely correct. If you are describing the process of maturing or the state of having matured (like a verb action or a descriptive phrase), then “grown up” (two words) is the appropriate choice. Imagine “grownup” as a completed individual, and “grown up” as the journey or result of growing.

Word	Part of Speech	Meaning	Example
Grownup	Noun, Adjective	An adult person; characteristic of an adult.	The grownup explained the rules to the children. She has a very grownup attitude.
Grown up	Verb Phrase (past participle), Phrasal Adjective	To have reached maturity; mature.	He has grown up a lot since last year. She is all grown up now.

How to Use Grownup

“Grownup” (one word) functions primarily as a noun, referring to an adult person. It can also be used as an adjective, meaning “adult” or “characteristic of an adult.” It often carries a slightly more informal or childlike tone when used as a noun, implying a contrast with children. As an adjective, it describes something that is mature or sophisticated.

Example 1: All the grownups gathered in the living room for a serious discussion.

Example 2: She bought a new dress for the party, feeling very grownup and elegant.

Example 3: The children were told to ask a grownup for help if they needed anything.

What are the different forms of Grownup?

As a noun, “grownup” forms its plural by adding “s”: grownups. As an adjective, it is generally used in its base form, though comparatives and superlatives can be formed with “more” and “most,” such as “more grownup” or “most grownup,” though these are less common than simply saying “more adult” or “very mature.”

Etymology of the word Grownup

The word “grownup” is a relatively modern compound, formed by combining the past participle “grown” and the adverb “up.” It emerged in the early 20th century, likely as a colloquial shortening of the phrase “grown-up person,” solidifying into a single word to function as a noun or adjective.

How to Use Grown up

“Grown up” (two words) serves two primary grammatical functions. Firstly, it is the past participle form of the phrasal verb “grow up,” meaning to mature or develop into an adult. When used in this way, it typically appears with an auxiliary verb (e.g., “have grown up,” “is grown up”). Secondly, it can function as a phrasal adjective, describing someone who has reached maturity or is mature.

Example 1: My little brother has grown up so much since I last saw him.

Example 2: She felt completely grown up after moving into her own apartment.

Example 3: He had always wanted to be an astronaut when he grown up.

What are the different forms of Grown up?

As the past participle of the phrasal verb “grow up,” its forms are derived from the verb “grow”:

• Base form: grow up
• Past tense: grew up
• Past participle: grown up
• Present participle: growing up

When used as a phrasal adjective, “grown up” remains in this form.

Etymology of the word Grown up

The phrase “grown up” originates from the verb “grow” (Old English growan, meaning “to sprout, flourish”) combined with the adverb “up.” The phrasal verb “grow up” has been in use for centuries, with the sense of reaching maturity becoming prominent by the 17th century. The past participle form “grown up” then naturally followed to describe the state of having matured.

Related Concepts

Understanding broader grammatical concepts helps clarify the distinction between “grownup” and “grown up.”

• Compound Nouns and Adjectives: “Grownup” is an example of a compound word, where two words are joined to create a new word with a distinct meaning. These can be written as one word (closed compound), two words (open compound), or hyphenated.
• Phrasal Verbs and Adjectives: “Grow up” is a phrasal verb, a combination of a verb and an adverb or preposition that creates a new meaning. “Grown up” also functions as a phrasal adjective, where the two words together modify a noun or pronoun.

Examples from Media and Literature

• “When you grow up, you tend to get told that the world is the way it is and your life is just to live your life inside the world. Try not to bash into the walls too much.” – Steve Jobs (using “grow up” as a verb phrase)
• “All children, except one, grow up.” – J.M. Barrie, Peter Pan (using “grow up” as a verb phrase)
• “Why can’t I be a grownup like you?” – A common line from a child in various films, using “grownup” as a noun.
• “It was a very grownup decision for someone so young.” – From a news article describing a mature choice, using “grownup” as an adjective.
• “She was all grown up and ready to face the world.” – A common narrative trope in novels and movies, using “grown up” as a phrasal adjective.

Practice Exercises

Choose the correct word to complete the sentence.

1. When I _____, I want to be an astronaut.
2. The children asked the _____ for another cookie.
3. She felt so _____ wearing her new formal gown.
4. He has _____ considerably since starting college.
5. It’s time you started making some _____ decisions.

Answer Key

1. grow up
2. grownup
3. grownup
4. grown up
5. grownup

Grownup Synonyms

Synonym	Definition
Adult	A fully developed person; relating to a mature person.
Mature	Having reached a state of full physical or mental development.
Responsible	Having an obligation to do something, or having control over or care for someone or something.
Sophisticated	Having or showing a refined taste or knowledge.

Grown up Synonyms

Synonym	Definition
Matured	Having completed the process of growth and development.
Developed	Having grown or caused to grow and become more advanced or elaborate.
Adult (as an adjective)	Fully developed and mature.
Full-grown	Having reached full size and maturity.

Frequently Asked Questions

Question 1: Is “grown-up” (hyphenated) also correct?
Yes, “grown-up” with a hyphen is also correct, especially when used as an adjective (e.g., “a grown-up conversation”) or sometimes as a noun. It often serves as an intermediate form between the two-word phrase “grown up” and the single-word compound “grownup.” All three forms are widely accepted, though “grownup” (one word) is increasingly common as a noun, and “grown up” (two words) as a verb phrase.

Question 2: Can “grownup” be used as an adjective?
Yes, “grownup” (one word) can certainly be used as an adjective to describe something as characteristic of an adult, mature, or sophisticated. For example, “She made a very grownup decision” or “It was a grownup party.”

Question 3: What’s the difference between “adult” and “grownup”?
While often interchangeable, “adult” is generally more formal and refers strictly to legal or biological maturity. “Grownup” (as a noun) is often used in a more informal context, especially when contrasting with children, and can sometimes carry a slightly playful or nostalgic connotation (“When I was a grownup…”). As adjectives, “adult” is neutral and factual, while “grownup” can imply a certain maturity or sophistication beyond mere age.

Conclusion

The distinction between “grownup” and “grown up” hinges on their grammatical roles. “Grownup” (one word) functions as a noun for an adult or an adjective meaning adult-like, while “grown up” (two words) is the past participle of the verb “grow up” or a phrasal adjective describing maturity. Understanding these differences allows for precise and correct communication. A pro tip for professional writing: When in doubt, consider the specific context and whether you need a noun/adjective or a verb phrase/phrasal adjective. Opting for clarity demonstrates linguistic competence and strengthens your professional reputation.