plum vs beach plum

plum and beach plum both are nouns.

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

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

plum: any of numerous varieties of small to medium-sized round or oval fruit having a smooth skin and a single pit
beach plum: small dark purple fruit used especially in jams and pies

Other hyponyms of plum include damson, damson plum, greengage, greengage plum, sloe, Victoria plum, cherry plum.

plum (noun)	beach plum (noun)
a highly desirable position or assignment	small dark purple fruit used especially in jams and pies
any of numerous varieties of small to medium-sized round or oval fruit having a smooth skin and a single pit	seacoast shrub of northeastern North America having showy white blossoms and edible purple fruit
any of several trees producing edible oval fruit having a smooth skin and a single hard stone

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