secret police vs constabulary

secret police and constabulary both are nouns.

Word	Noun	Adjective	Verb	Adverb
secret police	Yes	No	No	No
constabulary	Yes	No	No	No

As nouns, constabulary is a hypernym of secret police; that is, constabulary is a word with a broader meaning than secret police:

secret police: a police force that operates in secrecy (usually against persons suspected of treason or sedition)
constabulary: the force of policemen and officers

Other hypernyms of secret police include law, police, police force.

secret police (noun)	constabulary (noun)
a police force that operates in secrecy (usually against persons suspected of treason or sedition)	the force of policemen and officers