'unresistingly' originates from the prefix 'un-' (Old English), the verb 'resist' from Latin 'resistere', and the adverbial suffix '-ly' (Old English/Germanic), where 'un-' meant 'not', 'resistere' meant 'to stand back or oppose', and '-ly' formed adverbs meaning 'in the manner of'.

'resist' comes from Latin 'resistere', which passed into Old French/Anglo-Norman and Middle English (as forms like 'resisten'), then the adjective 'unresisting' was formed by prefixing Old English 'un-' to mean 'not resisting', and finally the adverb 'unresistingly' was formed by adding the suffix '-ly'.

Initially, the Latin root meant 'to stand back or oppose', but over time the negative construction 'unresistingly' evolved to mean 'without opposition' or 'passively', which is its current meaning.