'avidness' originates from Latin, specifically the adjective 'avidus', where 'avid-' meant 'eager' or 'desirous', and the English noun was formed by adding the suffix '-ness'.

'avidus' entered English via Late Latin (and influenced Middle French) as the adjective 'avid' in the late 16th century; the noun 'avidness' was later formed in English by combining 'avid' + '-ness'.

Initially it meant 'eager' or 'desirous' (often with a stronger, sometimes greedy sense); over time the sense broadened to include general keen interest or enthusiasm, sometimes without negative connotation.