damson vs plum

damson and plum both are nouns.

Word	Noun	Adjective	Verb	Adverb
damson	Yes	No	No	No
plum	Yes	No	No	Yes

As nouns, plum is a hypernym of damson; that is, plum is a word with a broader meaning than damson:

damson: dark purple plum of the damson tree
plum: any of numerous varieties of small to medium-sized round or oval fruit having a smooth skin and a single pit

damson (noun)	plum (noun)
dark purple plum of the damson tree	a highly desirable position or assignment
	any of numerous varieties of small to medium-sized round or oval fruit having a smooth skin and a single pit
	any of several trees producing edible oval fruit having a smooth skin and a single hard stone

damson (adverb)	plum (adverb)
	exactly
	completely; used as intensifiers