facet

Short definition from Wiktionary

Noun

1. 1
   Any one of the flat surfaces cut into a gem.
2. 2
   One among many similar or related, yet still distinct things.
3. 3
   One of a series of things, such as steps in a project.
4. 4
   One member of a compound eye, as found in insects and crustaceans.
5. 5
   A smooth circumscribed surface.
6. 6
   Any of the small joints at each segment of the spine that provide stability and help guide motion
7. 7
   The narrow plane surface between flutings of a column; a fillet.
8. 8
   A face of codimension 1 of a polytope.
9. 9
   A criterion that can be used to sort and filter, such as the colour or size of products in an online store.

Verb

1. 1
   To cut a facet into a gemstone.