'opposite-pinnate' originates from Latin, specifically the words 'oppositus' and 'pinnatus', where 'oppositus' meant 'placed against, set opposite' and 'pinna' meant 'feather' (giving 'pinnatus' = 'feathered' or 'having fins/feathers').

'opposite' came into English via Old French and Middle English from Latin 'opponere'/'oppositus' (meaning 'to place against'), while 'pinnate' entered botanical English from Late Latin 'pinnatus' (from 'pinna' 'feather'); the compound descriptive form 'opposite-pinnate' developed in botanical usage by combining these elements to describe leaf arrangement.

Initially, the elements meant 'placed against' (opposite) and 'feathered' (pinnate); over time they were joined in scientific/botanical English to mean specifically 'having pinnate leaves with leaflets arranged oppositely along the rachis', a narrower technical sense.