'unequal-toothed' originates from Modern English, formed by combining the adjective 'unequal' and the past-participle adjective 'toothed'; 'unequal' ultimately comes via Old French/Late Latin elements (from Latin 'aequalis' with a negating prefix) where the prefix 'un-'/negation meant 'not equal', and 'toothed' derives from Old English 'tōþ' meaning 'tooth'.

'unequal-toothed' developed as a compound in Middle/Modern English from 'unequal' (from Old French/Latin roots: Middle English/Old French forms meaning 'not equal') and 'toothed' (from Old English 'tōþ' -> Middle English 'tooth' with adjectival '-ed'), eventually becoming the modern hyphenated compound 'unequal-toothed'.

Initially a literal compound meaning 'having teeth that are not equal', the phrase has retained that literal sense but has been adopted in scientific descriptions to denote the technical concept similar to 'heterodont'.