synaptonemal complexPronunciation: /sɪˌnaptə(ʊ)ˈniːm(ə)l, sʌɪ-/Definition of synaptonemal complex noun Biology a ladder-like series of parallel threads visible in electron microscopy adjacent to and coaxial with pairing chromosomes in meiosis. Origin: 1950s: from synapto- (combining form of synapsis) + Greek nēma 'thread' + -alsynaptonemal complex in other Oxford dictionaries Definition of synaptonemal complex in the US English dictionary