'equal-leaved' originates from Modern English as a compound of the adjective 'equal' and the past-participial adjective-form of 'leaf' ('leaved'), where 'equal' ultimately comes from Latin 'aequalis' and 'leaf' comes from Old English 'lēaf'.

'equal' came into English via Latin 'aequalis' → Old French/Middle English forms (e.g. Middle English 'equale'/'equel') and became Modern English 'equal'; 'leaf' descended from Old English 'lēaf' → Middle English 'leaf' and the adjectival form 'leaved' developed in Modern English to mean 'having leaves'. The compound 'equal-leaved' was formed in Modern English botanical usage by combining these elements.

Initially, 'equal' meant 'level' or 'even' and 'leaf' meant the botanical 'leaf'; combined as 'equal-leaved' it has retained the specific botanical meaning 'having leaves of equal size or shape'.