traitorous

1. Having the character of a traitor; disloyal.
2. Constituting treason: a traitorous act. See synonyms at faithless.

adjective

1. Not true to duty or obligation: disloyal, faithless, false, false-hearted, perfidious, recreant, treacherous, unfaithful, untrue. See continue/stop/pause, trust/distrust.
2. Involving or constituting treason: seditious, treasonable, treasonous. See trust/distrust.

Definition: treacherous
Antonyms: faithful, loyal, patriotic

The adjective has 2 meanings:

Meaning #1: deliberately and abominably disloyal or likely to betray trust or confidence
  Synonyms: faithless, unfaithful

Meaning #2: constituting treason
  Synonyms: treasonable, treasonous