PI vs house dick

PI and house dick both are nouns.

Word	Noun	Adjective	Verb	Adverb
PI	Yes	No	No	No
house dick	Yes	No	No	No

As nouns, house dick is a hyponym of PI; that is, house dick is a word with a more specific, narrower meaning than PI:

PI: someone who can be employed as a detective to collect information and assist in criminal investigations
house dick: a private detective employed by a hotel or retail store

Other hyponyms of PI include hotel detective, house detective, inquiry agent, store detective.

PI (noun)	house dick (noun)
an antiviral drug used against HIV; interrupts HIV replication by binding and blocking HIV protease; often used in combination with other drugs	a private detective employed by a hotel or retail store
someone who can be employed as a detective to collect information and assist in criminal investigations
the scientist in charge of an experiment or research project