'multisyllabic' originates from Latin and Greek components: the prefix 'multi-' from Latin 'multus' meaning 'many', and 'syllabic' ultimately from Greek 'syllabē' (via Latin 'syllaba') meaning 'syllable'.

'multisyllabic' was formed in Modern English by combining the productive prefix 'multi-' with the adjective 'syllabic' (which entered English from Latin 'syllaba' via Old French, ultimately from Greek 'syllabē'), producing the modern adjective 'multisyllabic'.

Initially, it meant 'having many syllables', and over time this basic meaning has remained essentially the same in modern usage.