bow legs vs bow leg

bow legs and bow leg both are nouns.

Word	Noun	Adjective	Verb	Adverb
bow legs	Yes	No	No	No
bow leg	Yes	No	No	No

As nouns, bow legs and bow leg are synonyms defined as:

Other synonyms of bow legs include bandy legs.

bow legs (noun)	bow leg (noun)
outward curvature of the legs	a leg bowed outward at the knee (or below the knee)
	outward curvature of the legs