1. a thin, crisp cake or biscuit, often sweetened and flavored.
2. a thin disk of unleavened bread, used in the Eucharist, as in the Roman Catholic Church.
3. a thin disk of dried paste, gelatin, adhesive paper, or the like, used for sealing letters, attaching papers, etc.
4. Medicine/Medical. a thin sheet of dry paste or the like, used to enclose a powder to be swallowed.
5. any small, thin disk, as a washer or piece of insulation.
6. Electronics. a thin slice of semiconductor used as a base material on which single transistors or integrated-circuit components are formed.