lieutenant vs law officer

lieutenant and law officer both are nouns.

Word	Noun	Adjective	Verb	Adverb
lieutenant	Yes	No	No	No
law officer	Yes	No	No	No

As nouns, law officer is a hypernym of lieutenant; that is, law officer is a word with a broader meaning than lieutenant:

Other hypernyms of lieutenant include lawman, peace officer.

lieutenant (noun)	law officer (noun)
an officer in a police force	an officer of the law
a commissioned military officer
an assistant with power to act when his superior is absent
an officer holding a commissioned rank in the United States Navy or the United States Coast Guard; below lieutenant commander and above lieutenant junior grade