(1):
(n.) A double catalogue, containing in one part the names of living, and in the other of deceased, ecclesiastics and benefactors of the church; a catalogue of saints.
(2):
(n.) A picture or series of pictures painted on two tablets connected by hinges. See Triptych.
(3):
(n.) A writing tablet consisting of two leaves of rigid material connected by hinges and shutting together so as to protect the writing within.
(4):
(n.) Anything consisting of two leaves.