'irregularly-toothed' is a modern English compound formed from 'irregularly' + 'toothed'. 'Irregularly' derives from 'irregular' (Latin origin) with the adverbial suffix '-ly', and 'toothed' is the adjectival/past-participial form of 'tooth'.

'irregular' comes from Latin 'irregularis' (ir- 'not' + regularis 'according to rule') via Old French and Middle English; 'tooth' comes from Old English 'tōþ' (Proto-Germanic *tanþs) and later formed the adjective 'toothed' with the suffix -ed in Middle English. These elements combined in modern English to form descriptive compounds like 'irregularly-toothed'.

Initially the parts meant 'not regular' (ir-) and 'tooth' respectively; as a compound it has remained a descriptive term meaning 'having uneven or irregular teeth' and is used especially in botanical and zoological descriptions.