subcontinent vs landmass

subcontinent and landmass both are nouns.

Word	Noun	Adjective	Verb	Adverb
subcontinent	Yes	No	No	No
landmass	Yes	No	No	No

As nouns, landmass is a hypernym of subcontinent; that is, landmass is a word with a broader meaning than subcontinent:

subcontinent: a large and distinctive landmass (as India or Greenland) that is a distinct part of some continent
landmass: a large continuous extent of land

Other hypernyms of subcontinent include land mass.

subcontinent (noun)	landmass (noun)
a large and distinctive landmass (as India or Greenland) that is a distinct part of some continent	a large continuous extent of land