RN vs nurse clinician

RN and nurse clinician both are nouns.

Word	Noun	Adjective	Verb	Adverb
RN	Yes	No	No	No
nurse clinician	Yes	No	No	No

As nouns, nurse clinician is a hyponym of RN; that is, nurse clinician is a word with a more specific, narrower meaning than RN:

RN: a graduate nurse who has passed examinations for registration
nurse clinician: a registered nurse who has received special training and can perform many of the duties of a physician

Other hyponyms of RN include nurse-midwife, NP, nurse practitioner.

RN (noun)	nurse clinician (noun)
a graduate nurse who has passed examinations for registration	a registered nurse who has received special training and can perform many of the duties of a physician