Noun
subdiscipline (plural subdisciplines)
A field of study or work that is related to one aspect, but not the whole, of a broader field of study or work.
Social psychology is a subdiscipline of psychology.
Phonology is a subdiscipline of linguistics.
At many larger academic centers and university hospitals that excel in patient care and clinical research, urologists often specialize in a particular subdiscipline. Source: Internet
Nevertheless, it brought about the establishment of philosophy of science as a distinct subdiscipline of philosophy, with Carl Hempel playing a key role. Source: Internet