'undiscussed' is formed from the prefix 'un-' (meaning 'not') plus 'discussed', where 'discussed' comes from Latin 'discutere' (through Old French and Middle English).

'discutere' (Latin) → Old French 'discuter' → Middle English 'discussen'/'discus' → modern English 'discuss'; the negative prefix 'un-' derives from Old English 'un-' meaning 'not'. The compound 'un-' + 'discussed' produced 'undiscussed' in modern usage.

Originally Latin 'discutere' meant 'to shake apart; scatter' and later developed to mean 'to examine or debate'. The compound 'undiscussed' now means 'not examined or debated'.