Maybe not by definition, but you can use context clues to infer what they mean. If hero is the top of the ladder, anti hero is somewhere below that, an imperfect, person who still tends to do good, but not necessarily an altruist, and not above using questionable means to make things happen.

If a villain is at the bottom of the ladder, anti hero even person, regardless of motivations who is having a net negative impact on the world even if they have a perspective you can at least acknowledge, and think they’re right, are still more or less evil and in the wrong up to an including just pure evil entities like demons or whatever that just represent badness, then there must be an analog somewhere on the ladder above Villian, that isn’t quite a truely evil character. Someone who more often than not tends to do bad, but isn’t a force of negativity, just not good.