'Aonghus' originates from Old Irish, specifically the word 'Oengus' (also seen as 'Óengus'), where the elements 'oen/óen' meant 'one' and 'gus' meant 'choice, vigor, or strength'.

'Aonghus' changed from Old Irish 'Oengus/Óengus' and Middle Irish forms into the modern Irish spelling 'Aonghus'; it was anglicized as 'Aengus' and later as 'Angus' in English.

Initially it meant 'one-choice' or a compound conveying 'one' + 'strength/choice'; over time it became established primarily as a personal (given) name associated with a mythological figure, retaining the nuance of uniqueness or strength.