'avert' originates from Latin, specifically the word 'avertere' (variant of 'advertere'), where 'ab-/ad-' (a-) meant 'away/toward' and 'vertere' meant 'to turn'.

'avert' changed from Latin 'avertere' into Old French/Anglo-French forms and Middle English (e.g. 'averten') and eventually became the modern English word 'avert'; 'averter' is formed by adding the agentive suffix '-er' to the verb.

Initially, it meant 'to turn away' and over time it evolved to include the sense 'to prevent' (i.e., to turn away danger), which is reflected in modern usages.