Iago is most honest (II.iii.7) Othello, unaware of Iago's evil plans, comments on his honesty. This is most ironic, of course, since Iago is the furthest thing from it. Shakespeare is able to increase the tension of the plot with short, simple statements like this one.

Who steals my purse steals trash (III.iii.157) Iago has gotten Cassio drunk, and Cassio has gotten himself fired as Othello's lieutenant. He mourns the loss of his reputation, which, if compared to the theft of a purse, is more valuable than gold.

green-eyed monster (III.iii.166) Iago gives Othello very true advice in a sarcastic vein. Jealousy is compared to a "green-eyed monster." In the modern sense, the phrase is "green with envy."

vale of years (III.iii.266) Some critics believe this to be a reference to the 23rd Psalm: "Yea though I walk through the of the shadow of death." In the modern sense, it has been corrupted to vale of tears," meaning a painful experience.

Men should be what they seem; / Or those that be not, would they might seem none (III.iii.126-127) Probably the most bitingly ironic words in the play, Iago plants the idea in Othello's mind that Cassio might be cavorting with Desdemona, and is not "what he seems." Of course, it is plainly Iago who is not what he seems. Shakespeare adroitly uses this technique of having his villians describe what is in reality their own treachery, even when they are apparently referring to someone else. This only adds to the chilling, calculating nature of Iago.

foregone conclusion (III.iii.428) To Shakespeare, this phrase meant "a previous experiment." In the modern sense, it refers to something that has already been decided.

pomp and circumstance (III.iii.354) These are the celebrations that would be held in Cyprus for the victory over the Turks. In the modern sense, it is frequently used to describe a very formal event, such as an inauguration or graduation.

so sweet was never so fatal (V.ii.20) Othello is contemplating murdering Desdemona to save other men from her "deceit." Knowing how sweet Desdemona actually is means the real or spiritual death of a man.

Some bloody passion shakes your very frame (V.ii.44) In the play's final scene, Othello, broken and defeated by his complete submittal to Iago's plan, prepares to kill Desdemona and demands she admit her unfaithfulness. Of course, she has no idea what he is talking about, and says as much in this quote—hoping in vain that his rage is not to be imminently directed at her.

loved not wisely but too well (V.ii.345) Othello realizes too late that he was wrong about Desdemona's infidelity, but the only fault he admits is that he listened to Iago.

'tis the curse of service, / Preferment goes by letter and affection (I.i.35-36) In the first scene of Othello, we learn that Iago has been passed over in favor of Cassio for the position of Othello's lieutenant. This slight provides the motive for Iago's diabolical plan to wreak revenge on Othello. Here Iago complains that Cassio's elevation was based on favoritism, rather than traditional values of service and succession.

And will as tenderly be led by the nose / As asses are (I.iii.403-404) At the close of Act I, Iago hatches his plan against Othello. The theme of appearance and reality figures prominently throughout the play; here Iago notes that Othello is not adept at distinguishing between the two—making him more likely to fall victim to Iago's scheme.