WordNet (r) 3.0 (2006):

fit in
    v 1: go together; "The colors don't harmonize"; "Their ideas
         concorded" [syn: harmonize, harmonise, consort,
         accord, concord, fit in, agree]

Moby Thesaurus II by Grady Ward, 1.0:

30 Moby Thesaurus words for "fit in":
   accord, be there, belong, conform, correspond, dovetail,
   fall in with, fall into line, fit, follow the crowd,
   follow the fashion, follow the rule, get in line, go,
   go through channels, harmonize, have its place, have place,
   implant, infix, inlay, jibe, keep in step, pass muster,
   play the game, square, stay in line, tally, tessellate,
   toe the mark