'penult' originates as a clipped form of the English word 'penultimate', which ultimately comes from Latin 'paenultimus', where 'paene' meant 'almost' and 'ultimus' meant 'last'.

'penult' changed from the longer English adjective and noun 'penultimate' (from Latin 'paenultimus') by clipping the front part to form the shorter modern English term 'penult'.

Initially the Latin-rooted term meant 'almost last'; over time the clipped English form 'penult' came to be used specifically for 'the next-to-last syllable' in linguistic contexts.