'Subgroup' definitions:

Definition of 'subgroup'

From: WordNet
noun
A distinct and often subordinate group within a group
noun
(mathematics) a subset (that is not empty) of a mathematical group

Definition of 'Subgroup'

From: GCIDE
  • Subgroup \Sub"group`\, n. (Biol.) A subdivision of a group, as of animals. --Darwin. [1913 Webster]