childish
[adjective]
Synonyms: immature, boyish or girlish, foolish, infantile, juvenile, puerile, young

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Antonyms: adult
Related Words: asinine, fatuous, foolish, silly, simple, naive, unsophisticated, arrested, backward, moronic, retarded, slow, wanting

[TahlilGaran] English Synonym Dictionary ▲

child‧ish /ˈtʃaɪldɪʃ/ adjective

1. [usually before noun] relating to or typical of a child Antonym : adult:
a high childish laugh
her childish excitement

2. behaving in a silly way that makes you seem much younger than you really are – used to show disapproval Synonym : immature Antonym : mature:
Don’t be so childish!
I wish politicians would stop this childish name-calling.
► To describe someone who is as innocent, eager etc as a child, use childlike.
—childishly adverb
—childishness noun [uncountable]

[TahlilGaran] Dictionary of Contemporary English ▲