'polysyllabic' originates from Greek and Latin elements, specifically the Greek prefix 'poly-' (from Greek 'polús') meaning 'many' and the Greek word 'syllabē' (via Latin 'syllaba') meaning 'syllable'.

'polysyllabic' changed from Late Latin/Middle Latin formations such as 'polysyllabicus' and entered English via scholarly formation in Modern English, eventually becoming the modern English word 'polysyllabic'.

Initially it meant 'having many syllables', and over time it has retained that core meaning as 'composed of multiple syllables'.