Source : Webster's Revised Unabridged Dictionary (1913)

Posset \Pos"set\, n. [W. posel curdled milk, posset.]
   A beverage composed of hot milk curdled by some strong
   infusion, as by wine, etc., -- much in favor formerly. ``I
   have drugged their posset.'' --Shak.

Posset \Pos"set\, v. t. [imp. & p. p. {Posseted}; p. pr. & vb.
   n. {Posseting}.]
   1. To curdle; to turn, as milk; to coagulate; as, to posset
      the blood. [Obs.] --Shak.

   2. To treat with possets; to pamper. [R.] ``She was cosseted
      and posseted.'' --O. W. Holmes.

Source : WordNet®

posset
     n : sweet spiced hot milk curdled with ale or beer