French weed vs penny grass

French weed and penny grass both are nouns.

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

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

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

Other synonyms of French weed include fanweed, field pennycress, mithridate mustard, stinkweed, Thlaspi arvense.

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