Synonyms for Ratter (same or very similar meaning)
WordNet sense 1 (a disloyal person who betrays or deserts his cause or religion or political party or friend etc.):
apostate, deserter, recreant, renegade, turncoatWordNet sense 2 (any of several breeds of terrier developed to catch rats):
rat terrierFrom the ODE community, based on WordNetadd/edit