sell out (someone/something)

to stop being loyal to someone or something.

He accused Congress of selling out the American people to lawyers who opposed the bill.

I could sell you all out and go straight to the police with this information.

Usage notes: often money is the advantage that is gotten:

Anyone who would sell out his own country for money deserves to go to prison for life.

• balls-up
• banana republic
• banana skin
• Band-Aid
• bandwagon effect
• bandy about
• bandy something about
• bane of life
• bane of your life
• bang away
• bang for buck
• bang for the buck
• bang for your buck
• Bang goes!
• Bang goes something!
• bang the drum
• bang up job
• bank on
• bank on something
• baptism by fire
• baptism of fire
• bare-bones
• bare bones
• bare heart
• bare soul