Renegade, apostate, turncoat, recreant, backslider are strongly derogatory terms denoting a person who forsakes his faith or party, a cause, or an allegiance, and aligns himself with another.
Renegade, originally applied to a Christian who became a Mohammedan, came to mean one who completely denies all he has been brought up to believe by going over to the enemy or the opposition.
Apostate stresses the giving up, either voluntarily or under compulsion, of something (as one’s religious beliefs or political or intellectual principles) one has formerly professed and the acceptance of others which are usually, by implication, of a less exalted character.
Apostate therefore usually connotes surrender, but it need not, as renegade often does, imply treachery or hostility to what is forsaken.
Turncoat, a contemptuous designation, differs from renegade and apostate chiefly in its implications that profession of faith or allegiance is regarded lightly and that convenience or profit rather than conviction motivates the change.
Recreant, like apostate, implies a retreat from a stand one has taken, but it stresses cowardice and meanspiritedness, and usually connotes treachery to the party or cause once supported.
Backslider, in contrast to the other terms, usually implies a previous conversion and a reversion to the old indifference or the old beliefs; thus, a convert who goes back to his earlier state morally or to his earlier religious affiliation is regarded as a backslider by one adherent to the position he held as a convert.