plow vs ard plough

plow and ard plough both are nouns.

Word	Noun	Adjective	Verb	Adverb
plow	Yes	No	Yes	No
ard plough	Yes	No	No	No

As nouns, ard plough is a hyponym of plow; that is, ard plough is a word with a more specific, narrower meaning than plow:

plow: a farm tool having one or more heavy blades to break the soil and cut a furrow prior to sowing
ard plough: a simple light plough without a mouldboard.

Other hyponyms of plow include bull tongue, moldboard plow, mouldboard plough, ard, scratch plough.

plow (noun)	ard plough (noun)
a farm tool having one or more heavy blades to break the soil and cut a furrow prior to sowing	a simple light plough without a mouldboard.

plow (verb)	ard plough (verb)
act on verbally or in some form of artistic expression
to break and turn over earth especially with a plow
move in a way resembling that of a plow cutting into or going through the soil