'rebuttable' is formed in modern English by adding the suffix '-able' (meaning 'capable of') to the verb 'rebut', where 'rebut' comes from Old French 'rebuter' meaning 'to drive back, repel'.

'rebut' came into Middle English from Old French 'rebuter' (and related Old French forms, from 're-' + 'buter'/'bouter' meaning 'to push'), and later the English suffix '-able' (from Old French/Latin '-abilis') was added to form 'rebuttable'.

Originally related to the sense 'to drive or push back' (a physical repelling), the sense shifted to verbal/argumentative contexts and 'rebuttable' now means 'capable of being refuted or contradicted'.