Childish means behaving like a child when you should not. A childish remark, do not be childish, childish behaviour.
It is always critical when said of an adult. Childlike is the positive counterpart and means having the good qualities of a child — childlike wonder, childlike trust — and the pair is one of the neatest examples in English of the same idea split into praise and insult by the suffix. Of a child, childish simply means typical of children, with no criticism. Note childishly, and childishness.
1adjectivechildishBehaving like a child when you should not.
“The whole exchange was childish and went on for weeks.”
childish is a quality of immaturity.
Old English cildisc is child plus -isc, the ancestor of -ish. That ending has drifted towards mild disparagement in modern English — greenish, foolish, childish — while -like stayed neutral.
Middle English
childisch
English, today
childish
From Middle English childisch. From Middle English childisch, from Old English ċildisċ. by surface analysis, child + -ish.
Etymology from Wiktionary, CC BY-SA