'cardinalfish' originates from English, specifically the combination of the words 'cardinal' and 'fish', where 'cardinal' ultimately comes from Latin 'cardinalis' (from 'cardo') meaning 'principal' (later used as a name for bright red things) and 'fish' comes from Old English 'fisc' meaning 'fish'.

'cardinal' changed from Latin 'cardinalis' into Old/Middle English 'cardinal' and was later used as the name for the bright red bird (and as a color descriptor); 'fish' changed from Old English 'fisc' to the modern English 'fish'. The compound 'cardinal' + 'fish' was applied to small, often red, marine fishes (family Apogonidae).

Initially, 'cardinal' meant 'principal' (from Latin), but over time it acquired a color-related sense (associated with the bright red of a cardinal's robes) and was combined with 'fish' to denote small red or brightly colored fishes; the compound now names a specific group of fishes.