petty officer vs SCPO

petty officer and SCPO both are nouns.

Word	Noun	Adjective	Verb	Adverb
petty officer	Yes	No	No	No
SCPO	Yes	No	No	No

As nouns, SCPO is a hyponym of petty officer; that is, SCPO is a word with a more specific, narrower meaning than petty officer:

petty officer: a noncommissioned officer in the Navy or Coast Guard with a rank comparable to sergeant in the Army
SCPO: a senior noncommissioned officer in the Navy or Coast Guard with a rank comparable to master sergeant in the Army

Other hyponyms of petty officer include master-at-arms, senior chief petty officer.

petty officer (noun)	SCPO (noun)
a noncommissioned officer in the Navy or Coast Guard with a rank comparable to sergeant in the Army	a senior noncommissioned officer in the Navy or Coast Guard with a rank comparable to master sergeant in the Army