'monocephalous' originates from Greek, specifically the word 'monokephalós', where 'mono-' meant 'one' and 'kephalē' meant 'head'.

'monokephalós' passed into Neo-Latin as 'monocephalus/monocephalum' and was later adopted into English as 'monocephalous' (built from the Greek roots) with usage in scientific and descriptive contexts.

Initially it meant 'one-headed' in the literal, anatomical sense; over time it has retained that primary meaning while also gaining a figurative sense of 'single-headed' or 'centralized' leadership.