'irregular-toothed' is a compound of the adjective 'irregular' and the adjective 'toothed'. 'irregular' originates from Latin, specifically the word 'irregularis' (from 'in-' + 'regularis'), where 'in-' meant 'not' and 'regularis' related to 'regula' meaning 'rule'. 'toothed' derives from Old English 'toþ' (tooth) with the adjectival suffix '-ed'.

'irregular' passed into Old French and Middle English (e.g. Middle English 'irregulier') and eventually became modern English 'irregular'. 'tooth' came from Old English 'toþ', from Proto-Germanic '*tanþs'; the adjectival form 'toothed' developed in English by adding the suffix '-ed' to indicate 'having teeth'. Combined as a compound, 'irregular-toothed' follows modern English compounding patterns.

Individually, 'irregular' initially meant 'not governed by rule' and evolved to the general sense 'not regular' or 'uneven'; 'toothed' consistently meant 'having teeth'. Together the compound has kept the straightforward meaning 'having teeth that are not regular in form or arrangement'.