SSS vs independent agency

SSS and independent agency both are nouns.

Word	Noun	Adjective	Verb	Adverb
SSS	Yes	No	No	No
independent agency	Yes	No	No	No

As nouns, independent agency is a hypernym of SSS; that is, independent agency is a word with a broader meaning than SSS:

SSS: an independent federal agency that administers compulsory military service
independent agency: an agency of the United States government that is created by an act of Congress and is independent of the executive departments

SSS (noun)	independent agency (noun)
an independent federal agency that administers compulsory military service	an agency of the United States government that is created by an act of Congress and is independent of the executive departments