bow leg vs bow legs

bow leg and bow legs both are nouns.

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

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

Other synonyms of bow leg include bandy legs.

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