WordNet sense 1 (an abject coward):

craven, poltroon

WordNet sense 2 (a disloyal person who betrays or deserts his cause or religion or political party or friend etc.):

apostate, deserter, ratter, renegade, turncoat

WordNet sense 3 (deserting your allegiance or duty to leader or cause or principle):

disloyal

WordNet sense 4 (lacking courage; ignobly timid and faint-hearted):

cowardly, fearful