something imagined to be an extraordinary discovery but proving to be a delusion or a hoax: The announced cure for the disease was merely another mare's-nest.
2.
an extremely confused, entangled, or disordered place, situation, etc.: We just moved in, and the place is a mare's-nest.
a screen or mat covered with a dark material for shielding a camera lens from excess light or glare.
a chattering or flighty, light-headed person.
a gadget; dingus; thingumbob.
a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.
a children's mummer's parade, as on the Fourth of July, with prizes for the best costumes.
a printed punctuation mark (‽), available only in some typefaces, designed to combine the question mark (?) and the exclamation point (!), indicating a mixture of query and interjection, as after a rhetorical question.