Webster's Revised Unabridged Dictionary · 1913

Jack-o'-lantern

Jack-o'-lantern , noun

1.
(Biology) A large orange-colored luminescent mushroom, Clitocybe illudens, also classified as Omphalotus olearius. It is poisonous and is sometimes found on hardwood tree stumps.
2.
a pale light sometimes seen at night over marshy ground; an ignis fatuus; a will-o'-the-wisp
[Newspaper speculations] supplying so many more jack-o'-lanterns to the future historian. — Lowell
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.

Also: Jack-with-a-lantern