Mid 17th century; earliest use found in Obadiah Walker (1616–1699), college head and author. From multi- + syllable. Compare post-classical Latin multisyllabus, adjective.
Definition of multisyllable in US English:
multisyllable
nounˌmʌltɪˈsɪləbl
A polysyllable. rare.
adjectiveˌmʌltɪˈsɪləbl
= multisyllabic.
Origin
Mid 17th century; earliest use found in Obadiah Walker (1616–1699), college head and author. From multi- + syllable. Compare post-classical Latin multisyllabus, adjective.