'two-syllable' is a modern English compound of 'two' (from Old English 'twā', meaning 'two') and 'syllable' (originating from Greek 'syllabē' via Latin 'syllaba').

'syllable' changed from Greek 'syllabē' to Latin 'syllaba', passed into Old French and Middle English (var. 'sillable'/'syllable'), and in modern English it combined with 'two' to form the compound 'two-syllable'.

Initially, 'syllable' referred to a unit of spoken sound (from Greek meaning 'that which is taken together'); over time the compound 'two-syllable' has consistently meant 'having two syllables'.