Behaving like a child; childish, puerile, or somewhat immature in a way that's characteristic of young children.
From Scottish 'bairn' (child) plus the '-ish' suffix (meaning having qualities of), creating an adjective for childlike behavior or characteristics.
English uses '-ish' to make 'childish' but Scots gets to say 'bairnish'—it's a small linguistic choice that shows how different cultures describe child-like behavior with slightly different emotional flavors.
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