'equitably-treated' originates from Latin: 'equitably' from the Latin root 'aequus' meaning 'equal, fair' (via Old French 'equitable' and English suffix '-ly'), and 'treated' from Latin 'tractare' (from 'trahere') meaning 'to handle, draw.'

'equitable' came into English via Old French 'equitable' from Latin 'aequitas' and root 'aequus'; 'treat' entered English via Old French 'traiter' from Latin 'tractare'. The participial adjective phrase 'equitably treated' developed in Modern English and is often hyphenated as 'equitably-treated' when used attributively before a noun.

Initially, it meant 'treated in a fair or equal way,' and this meaning has remained stable in modern usage.