'flat-snouted' is a modern English compound formed from 'flat' and 'snout'. 'Flat' comes from Old English/Old Norse roots meaning 'level, even', and 'snout' derives from Middle English (from Old Norse/Old English words for the projecting nose or muzzle).

'flat' developed from older Germanic forms (Old Norse flatr / Old English cognates) and remained as 'flat' in Modern English; 'snout' evolved from Middle English 'snute'/'snout' (influenced by Old Norse 'snutr') into Modern English 'snout'; the compound adjective 'flat-snouted' arose in modern usage to describe animals with flattened muzzles.

Initially both elements referred to basic physical qualities ('flat' = level/plane; 'snout' = projecting nose); combined as a compound they have consistently meant 'having a flat snout' and retain that literal meaning (with occasional figurative use).