/sin"euh sis/ , n. Gram.
a construction in which an expected grammatical agreement in form is replaced by an agreement in meaning, as in The crowd rose to their feet, where a plural pronoun is used to refer to a singular noun.
[ 1890-95; sýnesis understanding, intelligence, equiv. to syn- SYN- + ( h ) e- (s. of hiénai to throw, send) + -sis -SIS ]