'straight-veined' originates from Modern English as a compound of 'straight' and 'veined', where 'straight' ultimately comes from Old English 'streht' (past participle related to 'streccan') meaning 'stretched/straight' and 'vein' comes from Latin 'vena' (via Old French 'veine') meaning 'vein'.

'straight' developed from Old English 'streht' (related to the verb 'streccan'), while 'vein' passed from Latin 'vena' to Old French 'veine' and into Middle English as 'vein'; these elements combined in Modern English to form the descriptive compound 'straight-veined'.

Initially the components referred literally to 'stretched/straight' and 'vein'; the compound has kept a literal, primarily botanical meaning of 'having straight veins'.