1.VerbUsed to express somewhat reluctant assent, saying that if one situation exists (or because it does exist), another event or situation that would otherwise be undesirable, difficult, impossible, etc., becomes more feasible or reasonable, or would not make a difference.
"You arrived too early, but since you're here, you might as well come in.; Macarons are very difficult to make, so you might as well make plentiful if you do decide to make any."
2.VerbUsed to liken one situation to another, typically saying that the existence of one situation is equivalent to the existence of another, usually more extreme, situation.
"You're going to tell her what I said about her? You might as well shoot me!; What a waste of time this has been. We might as well have stayed at home."
3.VerbUsed other than figuratively or idiomatically: see might, as well.