Verb
(idiomatic) Used 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.
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.
(idiomatic) Used 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.
You might as well fall flat on your face as lean over too far backward. James Thurber
The dead might as well try to speak to the living as the old to the young. Willa Cather
Trust your own instinct. Your mistakes might as well be your own, instead of someone else's. Billy Wilder
As long as you happen to put your hand in a container full of pickles, might as well dip your whole arm in the container. Malay Proverb
You might as well be hanged for a sheep as for a lamb. Australian Proverb
If you are going to walk on thin ice, you might as well dance. Eskimo Proverb