'suggestibly' ultimately derives from the verb 'suggest', which comes from Latin 'suggerere' (also seen as 'suggest-') where the prefix 'sub-' meant 'under' and 'gerere' meant 'to carry or bear'. The adjective 'suggestible' was formed from 'suggest' + the adjective-forming suffix '-ible', and the adverb 'suggestibly' from 'suggestible' + '-ly'.

'suggest' entered English via Old French and Late Latin (Latin 'suggerere' → Old French 'sugerer'/'suggérer') and Middle English 'suggesten'; from this came the adjective 'suggestible' in Modern English, which later produced the adverb 'suggestibly'.

Originally Latin 'suggerere' meant 'to bring under, to present, to put forward' (a physical or figurative carrying under/presenting). Over time the English 'suggest' came to mean 'to propose or put forward an idea', and derivatives like 'suggestible' evolved to mean 'capable of being influenced by such proposals'; the adverb 'suggestibly' carries that same sense of susceptibility.