'babyish' originates from English, specifically from the noun 'baby' combined with the adjectival suffix '-ish' (from Old English/West Germanic '-isc' meaning 'related to' or 'having the quality of').

'babyish' developed from Middle English/early modern English 'baby' (itself from earlier 'babe' or imitative 'bab-') plus the suffix '-ish'; 'babe'/'baby' -> 'baby' -> 'babyish'.

Initially it simply meant 'of or relating to a baby' (e.g., baby-like); over time it also acquired the extended sense of 'immature' or 'childishly foolish.'