common speedwell vs speedwell

common speedwell and speedwell both are nouns.

Word	Noun	Adjective	Verb	Adverb
common speedwell	Yes	No	No	No
speedwell	Yes	No	No	No

As nouns, speedwell is a hypernym of common speedwell; that is, speedwell is a word with a broader meaning than common speedwell:

common speedwell: common hairy European perennial with pale blue or lilac flowers in axillary racemes
speedwell: any plant of the genus Veronica

Other hypernyms of common speedwell include veronica.

common speedwell (noun)	speedwell (noun)
common hairy European perennial with pale blue or lilac flowers in axillary racemes	any plant of the genus Veronica