someone who is kept as a prisoner by an enemy so that the other side will do what the enemy demands [↪ kidnap]:
The group are holding two tourists hostage (=keeping them as hostages).
a family taken hostage at gunpoint
to be influenced and controlled by something, so that you are not free to do what you want:
Our country must not be held hostage to our past.
something that you have promised to do which may cause you problems in the future