infantile
[adjective]
Synonyms: childish, babyish, immature, puerile

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Antonyms: adult

[TahlilGaran] English Synonym Dictionary ▲

in‧fan‧tile /ˈɪnfəntaɪl/ adjective

1. infantile behaviour seems silly in an adult because it is typical of a child Synonym : childish:
infantile jokes

2. [only before noun] technical relating to or affecting babies and very young children:
infantile development

[TahlilGaran] Dictionary of Contemporary English ▲