plain vs moorland

plain and moorland both are nouns.

Word	Noun	Adjective	Verb	Adverb
plain	Yes	Yes	Yes	Yes
moorland	Yes	No	No	No

As nouns, moorland is a hyponym of plain; that is, moorland is a word with a more specific, narrower meaning than plain:

plain: extensive tract of level open land
moorland: open land usually with peaty soil covered with heather and bracken and moss

Other hyponyms of plain include flat, flood plain, floodplain, llano, moor, peneplain, peneplane, snowfield, steppe, tundra.

plain (noun)	moorland (noun)
a basic knitting stitch made by putting the needle through the front of the stitch from the lefthand side	open land usually with peaty soil covered with heather and bracken and moss
extensive tract of level open land

plain (adjective)	moorland (adjective)
not elaborate or elaborated; simple
lacking patterns especially in color
free from any effort to soften to disguise
clearly revealed to the mind or the senses or judgment
not mixed with extraneous elements
lacking embellishment or ornamentation
lacking in physical beauty or proportion

plain (verb)	moorland (verb)
express complaints, discontent, displeasure, or unhappiness

plain (adverb)	moorland (adverb)
unmistakably (`plain' is often used informally for `plainly')