'arenulous' originates from Latin, specifically the word 'arena', where 'arena' meant 'sand', and the Latin suffix elements '-ulus'/'-ulosus' (giving English '-ulous') conveyed the sense 'full of' or 'having the nature of'.

'arenulous' was formed from Latin/Neo-Latin adjective forms such as 'arenulosus' (derived from 'arena' + suffix) and was borrowed or created in English in post-medieval usage as 'arenulous'.

Initially, it meant 'full of or abounding in sand'; over time it has retained essentially the same meaning of 'sandy' or 'sand-covered' in modern usage.