black elder vs bourtree

black elder and bourtree both are nouns.

Word	Noun	Adjective	Verb	Adverb
black elder	Yes	No	No	No
bourtree	Yes	No	No	No

As nouns, black elder and bourtree are synonyms defined as:

black elder and bourtree: a common shrub with black fruit or a small tree of Europe and Asia; fruit used for wines and jellies

Other synonyms of black elder include common elder, elderberry, European elder, Sambucus nigra.

black elder (noun)	bourtree (noun)
a common shrub with black fruit or a small tree of Europe and Asia; fruit used for wines and jellies	a common shrub with black fruit or a small tree of Europe and Asia; fruit used for wines and jellies