'polyneuritic' is formed from the combining form 'poly-' (from Greek 'polús' meaning 'many') + 'neur-' (from Greek 'neûron' meaning 'nerve') + the adjectival suffix '-itic' (from Greek '-itēs' used to form names of inflammations or diseases).

'polyneuritic' derives from 'polyneuritis' (a modern medical formation from Greek elements) with the adjectival suffix '-ic'/'-itic' added to create an adjective describing the condition or its effects; thus the noun 'polyneuritis' gave rise to the adjective 'polyneuritic'.

Initially formed to mean 'pertaining to polyneuritis (inflammation of many nerves)', the word has retained that specialized medical meaning in modern usage.