put (an animal) out of its misery
idiomDefinition of put (an animal) out of its misery
: to kill (an injured or sick animal) so that it does not continue to suffer
—sometimes used to refer to people as well patients who are in constant pain and want to be put out of their misery —sometimes used humorously I know you're all anxious to hear the results, so let me put you out of your misery.