The Collaborative International Dictionary of English v.0.48:

Wassailer \Was"sail*er\, n.
   One who drinks wassail; one who engages in festivity,
   especially in drinking; a reveler.
   [1913 Webster]

         The rudeness and swilled insolence
         Of such late wassailers.                 --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

wassailer
    n 1: someone who enjoys riotous drinking [syn: wassailer,
         carouser]
    2: someone who proposes a toast; someone who drinks to the
       health of success of someone or some venture [syn: toaster,
       wassailer]