penny grass vs French weed

penny grass and French weed both are nouns.

Word	Noun	Adjective	Verb	Adverb
penny grass	Yes	No	No	No
French weed	Yes	No	No	No

As nouns, penny grass and French weed are synonyms defined as:

penny grass and French weed: foetid Eurasian weed having round flat pods; naturalized throughout North America

Other synonyms of penny grass include fanweed, field pennycress, mithridate mustard, stinkweed, Thlaspi arvense.

penny grass (noun)	French weed (noun)
foetid Eurasian weed having round flat pods; naturalized throughout North America	foetid Eurasian weed having round flat pods; naturalized throughout North America