'avgas' originates from English, specifically the phrase 'aviation gasoline', formed by contraction of 'aviation' + 'gas(oline)'.

'avgas' developed as a clipped/jargon form from the full phrase 'aviation gasoline' (and the intermediate spoken form 'av-gas'), and eventually became standardized in technical usage as 'avgas'.

Initially it referred directly to 'aviation gasoline'; over time the clipped form 'avgas' has maintained that same technical meaning.