Let's break it down:
* Quench: To extinguish a fire or flame by pouring water or another liquid onto it.
* D: This is a shortened form of "it", referring to a candle.
The phrase "quench'd d" therefore means "extinguished it (the candle)".
Context: This phrase appears in Act 2, Scene 1 of Macbeth. Lady Macbeth is trying to calm Macbeth after he has just murdered King Duncan. She is trying to convince him that the deed is done and they should move on. She says:
> **"Infected be the air within. /
> What, though the flame of life be quench'd d /
> The breath of life? "**
In this context, Lady Macbeth is comparing the candle to the King's life, saying that even though the candle (life) has been extinguished, they must move on.
The use of "quench'd d" emphasizes the finality of the King's death, adding to the sense of darkness and guilt that pervades the play.