cattle grid vs cattle guard

cattle grid and cattle guard both are nouns.

Word	Noun	Adjective	Verb	Adverb
cattle grid	Yes	No	No	No
cattle guard	Yes	No	No	No

As nouns, cattle grid and cattle guard are synonyms defined as:

cattle grid and cattle guard: a bridge over a ditch consisting of parallel metal bars that allow pedestrians and vehicles to pass, but not cattle

cattle grid (noun)	cattle guard (noun)
a bridge over a ditch consisting of parallel metal bars that allow pedestrians and vehicles to pass, but not cattle	a bridge over a ditch consisting of parallel metal bars that allow pedestrians and vehicles to pass, but not cattle