'isognathous' originates from Ancient Greek, specifically the elements 'isos' and 'gnathos', where 'isos' meant 'equal' and 'gnathos' meant 'jaw'.

'isognathous' passed into New Latin/Modern scientific usage from Greek (compare Greek 'isognathos') and was adopted into English technical vocabulary in zoological and anatomical descriptions.

Initially it meant 'equal-jawed' in a literal sense; over time the term has remained specialized and is chiefly used to describe anatomical symmetry of the jaws.