'assistless' originates from English, specifically the combination of 'assist' and the suffix '-less', where 'assist' ultimately comes from Latin 'assistere' (via Old French 'assister') meaning 'to stand by' and '-less' comes from Old English 'lēas' meaning 'without'.

'assist' changed from Latin 'assistere' to Old French 'assister', then entered Middle English as forms like 'assisten' and eventually became modern English 'assist'. The suffix '-less' changed from Old English 'lēas' to Middle English '-les' and then to the modern English suffix '-less', and the compound formation produced 'assistless'.

Initially, the root meant 'to stand by' (assist) and the suffix meant 'without'; over time the compound came to mean simply 'without assistance' in modern usage.