'conjugate' originates from Latin, specifically the word 'coniugatus' / 'coniugare', where 'con-' meant 'together' and the root related to 'iug-' (from 'iungere') meant 'to join'.

'conjugate' changed from Latin 'coniugare' into Old French 'conjuguer' and then entered Middle English as forms like 'conjugaten', eventually becoming the modern English 'conjugate'.

Initially, it meant 'to join together' (literally, as in marriage or joining), but over time it developed specialized senses such as 'to join with endings' in grammar (to inflect a verb) and the chemical sense of 'linked/alternating' bonds.