The headword -- third person singular, imperfect, of sunakma/zw -- has the same glossing in the Synagoge and Photius' Lexicon; it must be quoted from somewhere. Elsewhere in the Suda it can refer simply to the synchronicity between one individual and another (iota 399, iota 467), but in the present instance the gloss suggests a different context -- perhaps Josephus, Jewish War 5.424, on the mentality of conspirators (web address 1).