'assubjugate' originates from Latin, specifically the word 'assubjugare', where the prefix 'ad-' (assimilated to 'as-') meant 'to/toward' and 'subjugare' meant 'to put under a yoke' (from Latin 'sub-' = 'under' + 'jugum' = 'yoke').

'assubjugare' in Latin influenced Old French and later Middle English forms (compare Old French assoujagier / assujugier), and the element merged with forms of 'subjugate' to yield the English 'assubjugate' (now rare/archaic compared with 'subjugate').

Initially it meant literally 'to put under a yoke' (a physical yoking); over time it broadened to the figurative sense 'to bring under control or domination', matching the modern sense.