jack-with-a-lantern

 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 1.5]

 a pale light sometimes seen at night over marshy ground; an ignis fatuus; a will-o'-the-wisp  [WordNet 1.5]

 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]