interpolation vs subject matter

interpolation and subject matter both are nouns.

Word	Noun	Adjective	Verb	Adverb
interpolation	Yes	No	No	No
subject matter	Yes	No	No	No

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

Other hypernyms of interpolation include content, message, substance.

interpolation (noun)	subject matter (noun)
the action of interjecting or interposing an action or remark that interrupts	content communicating a message; what something is about
(mathematics) calculation of the value of a function between the values already known
a message (spoken or written) that is introduced or inserted