Wordnet 3.0
NOUN (1)
1. 
 a cookout at the seashore where clams and fish and other foods are cooked--usually on heated stones covered with seaweed; 
The Collaborative International Dictionary of English v.0.48:
Clambake \Clam"bake\, n.
   The backing or steaming of clams on heated stones, between
   layers of seaweed; hence, a picnic party, gathered on such an
   occasion.
   [1913 Webster]
WordNet (r) 3.0 (2006):
clambake
    n 1: a cookout at the seashore where clams and fish and other
         foods are cooked--usually on heated stones covered with
         seaweed
Moby Thesaurus II by Grady Ward, 1.0:
36 Moby Thesaurus words for "clambake":
   $100-a-plate dinner, TV dinner, alfresco meal, barbecue, breakfast,
   brunch, buffet supper, campaign dinner, campaigning, coffee break,
   cookout, diner, dinner, electioneering, elevenses, fish fry,
   fund-raising dinner, high tea, hot luncheon, lunch, luncheon, mash,
   meat breakfast, petit dejeuner, picnic, politicking, rally,
   stumping, supper, tea, tea break, teatime, tiffin,
   whistle-stopping, wiener roast, wienie roast