'equal-winged' originates from Modern English, specifically the compound of the adjective 'equal' and the past-participial/adjectival form 'winged', where 'equal' meant 'even, level' and 'winged' meant 'having wings'.

'equal' comes from Latin 'aequalis' (via Old French/Norman 'equal'), where 'aequalis' meant 'level, equal'; 'wing' comes from Old English 'wenge' (from Proto-Germanic *winguz), meaning 'wing', and the adjectival form 'winged' developed from the past participle of the verb 'to wing' in Middle/Modern English. The modern compound 'equal-winged' formed in English by combining these elements.

Initially the components meant 'even/level' (from 'equal') and 'having wings' (from 'winged'); combined, the compound has maintained the straightforward meaning of 'having wings that are equal' with little semantic shift.