v. 25B6; verb
he betrayed his own brother : BREAK ONE'S PROMISE TO, be disloyal to, be unfaithful to, break faith with, play someone false; inform on/against, give away, denounce, sell out, stab in the back; informal split on, rat on, peach on, stitch up, do the dirty on, sell down the river, squeal on; Brit. informal grass on, shop, sneak on; N. Amer. informal rat out, drop a/the dime on, finger; Austral./NZ informal dob on, point the bone at.
he betrayed a secret : REVEAL, disclose, divulge, tell, give away, leak; unmask, expose, bring out into the open; let slip, let out, let drop, blurt out; informal blab, spill.
be loyal to, hide.