girth vs circumference

girth and circumference both are nouns.

Word	Noun	Adjective	Verb	Adverb
girth	Yes	No	Yes	No
circumference	Yes	No	No	No

As nouns, circumference is a hypernym of girth; that is, circumference is a word with a broader meaning than girth:

Other hypernyms of girth include perimeter.

girth (noun)	circumference (noun)
stable gear consisting of a band around a horse's belly that holds the saddle in place	the size of something as given by the distance around it
the distance around a person's body	the length of the closed curve of a circle
	the boundary line encompassing an area or object

girth (verb)	circumference (verb)
tie a cinch around