'arietta' originates from Italian, specifically the word 'arietta', where the suffix '-etta' meant 'small' (a diminutive).

'arietta' entered English from Italian (via musical usage) as a diminutive of 'aria'; 'aria' itself comes from Italian/Latin 'aria' meaning 'air' or 'melody'.

Initially it meant 'little aria' in Italian, and in English musical usage it has retained the meaning of a short or simple aria.