In Shakespeare's Macbeth, equivocation plays a central part in bringing about the death of Macbeth.
Equivocation is defined as...
...the misleading use of a term with more than one meaning...
It can also be described as "doublespeak" or "doubletalk," which is…
...language that deliberately disguises, distorts, or reverses the meaning of words.
Its use in Macbeth is intentional, and it refers primarily to the second set of predictions given by the witches. With the first set of predictions, the witches lure him with small truths: calling him by his present title, Glamis, his upcoming "promotion" with an added title of "thane of Cawdor," and finally with the clincher, the man who will be king. (This last prediction might be included as a form of equivocation—they fail to mention that in order to be king, Macbeth must first murder Duncan.)
When Hecate, the queen of the witches, learns that the witches have been trafficking with Macbeth, but only playing with him, she is angry. She wants to be a part of the "fun," and she believes that the evil they serve has not been "uplifted" in any way—she tells the weird sisters that they must make sure to lure Macbeth to his ultimate destruction.
It is here that we remember Banquo's warning to Macbeth when he told his friend that the powers of evil win a man with small truths, and then trick him with the big lie—the one that makes all the difference—when he already is a believer in the truth of their words…
...But ’tis strange;
And oftentimes, to win us to our harm,
The instruments of darkness tell us truths,
Win us with honest trifles, to betray's
In deepest consequence— (I.iii.132-136)
As Banquo warned Macbeth in Act One, there is little truth to what the witches predict in Act Four; Macbeth will learn too late that he has been deceived.
Foolishly, Macbeth thinks he can control the witches. They serve a darker power, but they let he think he can command them. When Macbeth demands new predictions, they equivocate.
Each new prediction is delivered by an apparition or vision, and it says to watch out for Macduff—this is true enough:
Macbeth! Macbeth! Macbeth! Beware Macduff;
Beware the Thane of Fife. (IV.i.79-80)
The second apparition "reels" a "hooked" Macbeth in; the vision tells Macbeth that only a man born of a woman can harm him. Literally, all men are born of a woman, but technically, a child can be "born" in more than one way. This is where they trick Macbeth:
Be bloody, bold, and resolute; laugh to scorn
The power of man, for none of woman born
Shall harm Macbeth. (88-90)
Macbeth thinks he's safe, sure there is no one who does not fit that description. Later, Macduff will tell Macbeth that he was "born" by caesarean section.
The final apparition reinforces Macbeth's "false sense of security." This vision says that Macbeth will never be defeated until the woods can move to the hill. Macbeth figures woods cannot move. However, the technicality here is that Malcolm's army will camouflage itself with tree branches, so it looks as if the woods are moving.
…Macbeth shall never vanquish’d be until
Great Birnam Wood to high Dunsinane Hill
Shall come against him. (103-105)
These equivocations lure Macbeth to his doom for he unwisely forgets the nature of the "women" who advise him. By the time he realizes this, it is too late.