Discharge in more ways than one (6)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Multiple definitions, because “let off” can mean “discharge” in several ways (though some of them are probably related). To fire a gun or explosive charge; to release someone from employment or from a commitment; to release waste gases, as in “let off steam”; and I suppose if someone is charged with a criminal offence and then let off without going to trial, they could be said to be dis-charged.