Does Hamlet already suspect that the cup is poisoned? His repeated refusals to drink, his exclamation “Good madam!” when his mother drinks, and his deep suspicion of Claudius suggest that he probably does.

However, Hamlet is also skeptical of drinking and carousing (see note below), and he at least acts surprised when the poisoning is revealed:

O villainy! Ho! let the door be lock’d:
Treachery! Seek it out.

Fat here most likely means “sweaty,” as indicated by Gertrude’s tossing Hamlet her “napkin” (handkerchief).

In 2015 Slate ran an entire article (“Is Hamlet Fat?”) dissecting this line and the speculations it’s prompted over the years.

scant of breath: short of breath.

rapiers: fencing swords (the kind Hamlet and Laertes are fighting with).

poniards (a.k.a. poignards): long thrusting knives or daggers.

Spanish cup-hilt rapier. Wikimedia

Poignard. Wikimedia/Birmingham Museums Trust

imponed: a fancy word for “staked” or “wagered.” Hamlet mocks its fanciness below.

Samuel Johnson notes in his 1765 commentary:

…perhaps imponed is pledged, impawned, so spelt to ridicule the affectation of uttering English words with French pronunciation.

Barbary (a.k.a. Berber or Barb) horses are a breed of sport horse from the North African region formerly called the Barbary Coast.

Barbary horses are mentioned several times in Shakespeare; Iago nastily compares Othello to one in Othello 1.1, while Richard II contains an affectionate reference (5.5):

KING RICHARD II: Rode he on Barbary? Tell me, gentle friend,
How went he under him?

GROOM: So proudly as if he disdain’d the ground.

In Shakespeare’s England (1916), A. Forbes Sieveking speculated (with no evidence) that the horse may have had personal significance for Shakespeare:

Of all these, the Barbary horse or Barb was undoubtedly Shakespeare’s favourite. With such affection and intimacy does he dwell upon its merits that it is probable that the poet at one time possessed a roan barb.

Barbary horses in Théodore Géricault’s Riderless Racers at Rome (1817)

For glosses, see notes on Osric’s speech above.

Hamlet again throws Osric’s flowery phrasing back at him with “liberal-conceited carriages.”

laid: wagered.

passes: rounds.

Claudius has apparently bet that Laertes won’t beat Hamlet by more than three hits. However, the meaning isn’t completely clear. The Riverside Shakespeare notes:

Not satisfactorily explained despite much discussion. One suggestion is that Laertes has raised the odds against himself by wagering that out of twelve bouts he will win nine.

Here’s Samuel Johnson’s cranky note from 1765:

This wager I do not understand. In a dozen passes one must exceed the other more or less than three hits. Nor can I comprehend, how, in a dozen, there can be twelve to nine. The passage is of no importance; it is sufficient that there was a wager. The quarto has the passage as it stands. The folio, He hath one twelve for mine.

In other words, win under the favorable terms of the wager, which favor Hamlet (the king has bet that Laertes won’t beat him by more than three hits).

trial: combat.

By “vouchsafe the answer” Osric means “stand as Laertes’s opponent,” thus answering the challenge.

Hamlet plays on “answer” by retorting, How if I answer ‘no’? In other words, What if I just refuse the match?