cockle-bur vs cockle-burr

cockle-bur and cockle-burr both are nouns.

Word	Noun	Adjective	Verb	Adverb
cockle-bur	Yes	No	No	No
cockle-burr	Yes	No	No	No

As nouns, cockle-bur and cockle-burr are synonyms defined as:

cockle-bur and cockle-burr: any coarse weed of the genus Xanthium having spiny burrs

Other synonyms of cockle-bur include cocklebur, cockleburr.

cockle-bur (noun)	cockle-burr (noun)
any coarse weed of the genus Xanthium having spiny burrs	any coarse weed of the genus Xanthium having spiny burrs