white pepper vs peppercorn

white pepper and peppercorn both are nouns.

Word	Noun	Adjective	Verb	Adverb
white pepper	Yes	No	No	No
peppercorn	Yes	No	No	No

As nouns, peppercorn is a hypernym of white pepper; that is, peppercorn is a word with a broader meaning than white pepper:

white pepper: pepper ground from husked peppercorns
peppercorn: pungent seasoning from the berry of the common pepper plant of East India; use whole or ground

Other hypernyms of white pepper include pepper.

white pepper (noun)	peppercorn (noun)
pepper ground from husked peppercorns	pungent seasoning from the berry of the common pepper plant of East India; use whole or ground
climber having dark red berries (peppercorns) when fully ripe; southern India and Sri Lanka; naturalized in northern Burma and Assam