facet

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. One of the flat polished surfaces cut on a gemstone or occurring naturally on a crystal.
2. n. Anatomy A small, smooth, flat surface, as on a bone or tooth.
3. n. Biology One of the lenslike visual units of a compound eye, as of an insect.
4. n. One of numerous aspects, as of a subject. See Synonyms at phase.

Century Dictionary and Cyclopedia

1. n. A little face; a small surface; specifically, in lapidary work, a small polished surface, usually of some geometrical form; one of the many variously shaped segments or faces into which the surface of a gem is broken in order to increase its brilliancy. There are various arrangements of the facets, the choice depending upon the shape of the stone, but they may be grouped in three classes, styled brilliant cut, rose cut, and trap cut. See cuts under brilliant.
2. n. In architecture the fillet between the flutings of a column.
3. n. In anatomy, a smooth, flat, circumscribed articular surface of bone. See second cut under dorsal.
4. n. In entomology, the surface of an ocellus of the compound eye of an insect; also, an ocellus.
5. To cut a facet or facets upon: as, to facet a diamond.
6. n. A book; especially, a child's book of instruction; a primer.
7. n. In the embryo of Pentastomum, the circular thickening left on the detached integument at the site of the dorsal cone after the separation of the embryo from the integument. Also facette. Compare cervical cross.

Wiktionary

1. n. Any one of the flat surfaces cut into a gem.
2. n. One among many similar or related, yet still distinct things.
3. n. One of a series of things, such as steps in a project.
4. n. anatomy One member of a compound eye, as found in insects and crustaceans.
5. n. mathematics A face of codimension 1 of a polytope.
6. v. To cut a facet into a gemstone.

GNU Webster's 1913

1. n. A little face; a small, plane surface.
2. n. (Anat.) A smooth circumscribed surface.
3. n. (Arch.) The narrow plane surface between flutings of a column.
4. n. (Zoöl.) One of the numerous small eyes which make up the compound eyes of insects and crustaceans.
5. v. To cut facets or small faces upon.

WordNet 3.0

1. n. a smooth surface (as of a bone or cut gemstone)
2. n. a distinct feature or element in a problem