arena vs realm

arena and realm both are nouns.

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

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

arena (noun)	realm (noun)
a playing field where sports events take place	a knowledge domain that you are interested in or are communicating about
a large structure for open-air sports or entertainments	the domain ruled by a king or queen
the central area of an ancient Roman amphitheater where contests and spectacles were held; especially an area that was strewn with sand	a domain in which something is dominant
a particular environment or walk of life