In linguistics, a proparoxytone (Greek: προπαροξύτονος, proparoxýtonos) is a word with stress on the antepenultimate (third last) syllable, such as the English words "cinema" and "operational". Related concepts are paroxytone (stress on the penultimate syllable) and oxytone (stress on the last syllable).
In English, most nouns of three or more syllables are proparoxytones, except in words ending in –tion or –sion, which tend to be paroxytones (operation, equivocation). This tendency is so strong in English that it frequently leads to the stress on derived words being on a different part of the root. For example, the root photograph gives rise to the nouns photography and photographer, family → familiar and familial. (In many dialects of English, the i in family is even deleted entirely, and still has the stress in familial and familiar.)
In medieval Latin lyric poetry, a proparoxytonic line or half-line is one where the antepenultimate syllable is stressed, as in the first half of the verse "Estuans intrinsecus || ira vehementi."