'two-formed' originates from Old English and Latin roots, specifically the Old English word 'twā' for 'two' and Latin 'forma' where 'forma' meant 'shape' or 'appearance'.

'two-formed' developed in Modern English as a compound of 'two' + past participle/adjective 'formed' (from Latin 'formare' via Old French/Old English influence). It is analogous in concept to older compounds like 'twofold' and to learned formations using Latin 'bi-' or 'biform', and eventually stabilized as the hyphenated adjective 'two-formed'.

Initially it simply described something 'formed in two ways' and over time it has retained that core sense, often used more narrowly in technical contexts (e.g., biology, morphology, or grammar) to mean 'occurring in two distinct forms'.