outgroup

Etymology
From.

Noun

 * 1)  The group of people who do not belong to one's own social group.
 * 2)  In cladistics, all the taxa included in a study that do not belong to the ingroup that is of immediate interest.
 * 3) * 2009 January 15, Martin D. Brazeau, “The braincase and jaws of a Devonian 'acanthodian' and modern gnathostome origins”, Nature Volume 457 No. 7227, doi:10.1038/nature07436:
 * A cladistic analysis of 45 ingroup and two outgroup taxa was performed on the basis of 134 characters.

Verb

 * 1) To form an outgroup.