arena vs circus

arena and circus both are nouns.

Word	Noun	Adjective	Verb	Adverb
arena	Yes	No	No	No
circus	Yes	No	No	No

As nouns, circus is a hyponym of arena; that is, circus is a word with a more specific, narrower meaning than arena:

arena: a playing field where sports events take place
circus: an arena consisting of an oval or circular area enclosed by tiers of seats and usually covered by a tent

As nouns, circus is a hyponym of arena; that is, circus is a word with a more specific, narrower meaning than arena:

arena: a large structure for open-air sports or entertainments
circus: (antiquity) an open-air stadium for chariot races and gladiatorial games

arena (noun)	circus (noun)
a playing field where sports events take place	a performance given by a traveling company of acrobats, clowns, and trained animals
a large structure for open-air sports or entertainments	a frenetic disorganized (and often comic) disturbance suggestive of a large public entertainment
the central area of an ancient Roman amphitheater where contests and spectacles were held; especially an area that was strewn with sand	an arena consisting of an oval or circular area enclosed by tiers of seats and usually covered by a tent
a particular environment or walk of life	(antiquity) an open-air stadium for chariot races and gladiatorial games
	a travelling company of entertainers; including trained animals