communications vs subject area

communications and subject area both are nouns.

Word	Noun	Adjective	Verb	Adverb
communications	Yes	No	No	No
subject area	Yes	No	No	No

As nouns, subject area is a hypernym of communications; that is, subject area is a word with a broader meaning than communications:

communications: the discipline that studies the principles of transmitting information and the methods by which it is delivered (as print or radio or television etc.)
subject area: a branch of knowledge

Other hypernyms of communications include bailiwick, discipline, field, field of study, study, subject, subject field.

communications (noun)	subject area (noun)
the discipline that studies the principles of transmitting information and the methods by which it is delivered (as print or radio or television etc.)	a branch of knowledge