A reciprocal, parallel or complementary relationship between two or more comparable objects.
An isomorphism from a projective space to the dual of a projective space, often to the dual of itself.
One of the several measures of the linear statistical relationship between two random variables, indicating both the strength and direction of the relationship.
A word or phrase with a meaning that is the same as, or very similar to, another word or phrase.
An alternative (often shorter) name defined for an object in a database.
Any name for a taxon, usually a validly published, formally accepted one, but often also an unpublished name.
A word whose meaning is the same as that of another word.
Any of the formal names for a taxon, including the valid name (i.e. the senior synonym).