n. 1. (Biol.) A large orange-colored luminescent mushroom, Clitocybe illudens, also classified as Omphalotus olearius. It is poisonous and is sometimes found on hardwood tree stumps. [ wns=1 ]
Syn. -- jack-a-lantern, Clitocybe illudens. [ WordNet 1.5 +PJC ]

2. a pale light sometimes seen at night over marshy ground; an ignis fatuus; a will-o'-the-wisp. [ wns=2 ]“[ Newspaper speculations ] supplying so many more jack-o'-lanterns to the future historian.” Lowell.
Syn. -- friar's lantern, ignis fatuus, will-o'-the-wisp. [ WordNet 1.5 ]

3. A lantern carved from a hollowed-out pumpkin, with holes cut in the rind and so shaped that when it is illuminated by a candle inside, the features of a human face, cat's face, etc. appear in a glowing yellow color. It is used mostly as a decoration at Halloween. [ WordNet 1.5 +PJC ]