'isognathism' originates from Greek, specifically from the elements 'isos' and 'gnathos', where 'isos' meant 'equal' and 'gnathos' meant 'jaw'; the suffix '-ism' denotes 'state or condition'.

'isognathism' was formed in New Latin/technical usage from Greek roots (compare New Latin 'isognathismus') and was adopted into English scientific vocabulary with essentially the same form 'isognathism'.

Initially, it meant 'the state of having equal jaws', and this technical meaning has been retained in modern anatomical and paleontological usage.