facet

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

This facet of the diamond was masterfully cut to enhance its value.
The child's learning disability was only one facet of the problems contributing to his delinquency.
We had just about completed the research facet of the project when the order came to cancel it.
the articular facet of a bone