'irregular-leaved' originates from a combination of 'irregular' and 'leaf'. 'Irregular' comes from Latin via Old French, specifically from Latin 'irregularis', where the prefix 'in-'/ 'ir-' meant 'not' and 'regularis' related to 'regula' meaning 'rule'. 'Leaf' originates from Old English 'lēaf'.

'irregular' entered English from Old French 'irregulier' and ultimately from Latin 'irregularis'; 'leaf' developed from Old English 'lēaf' to Middle English 'leaf' and then modern English 'leaf'. The compound form 'irregular-leaved' arose in English botanical usage by combining these elements to describe leaf characteristics.

Initially the parts meant 'not according to rule' + 'leaf', and over time the compound came to be used specifically in botanical contexts to mean 'having leaves that are irregular in shape, size, or arrangement.'