from
The Collaborative International Dictionary of English v.0.48
Jack-o'-lantern \Jack"-o'-lan`tern\, Jack-with-a-lantern
\Jack"-with-a-lan`tern\, 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. [WordNet sense 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. [WordNet sense
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]