'nonphonetic' originates from the English prefix 'non-' (from Latin 'non' meaning 'not') combined with 'phonetic,' which ultimately comes from Greek 'phonētikos' from 'phonē' meaning 'voice' or 'sound'.

'phonetic' came from Greek 'phonētikos' → Latin 'phoneticus' → French 'phonétique' → Middle English 'phonetic'; the modern English adjective 'nonphonetic' formed by adding the English prefix 'non-' to 'phonetic'.

Initially elements meant 'not' (non-) and 'relating to sound/voice' (phonetic); over time 'nonphonetic' came to be used specifically to mean 'spelling or writing that does not match pronunciation' in modern usage.