'Aquilius' originates from Latin, specifically the word 'aquila', where the root 'aquil-' meant 'eagle'.

'Aquilius' was used in Classical Latin as a family name (nomen); it continued in Medieval and Renaissance Latin texts and was adopted into English usage as the proper name 'Aquilius' when referring to Roman individuals or literary/historical figures.

Initially, it meant 'of the eagle' or 'eagle-like' (deriving from 'aquila'), but over time it evolved into primarily a hereditary family name rather than a descriptive term.