hart vs elk

hart and elk both are nouns.

Word	Noun	Adjective	Verb	Adverb
hart	Yes	No	No	No
elk	Yes	No	No	No

As nouns, elk is a hypernym of hart; that is, elk is a word with a broader meaning than hart:

Other hypernyms of hart include American elk, Cervus elaphus, red deer, wapiti.

hart (noun)	elk (noun)
a male deer, especially an adult male red deer	large northern deer with enormous flattened antlers in the male; called `elk' in Europe and `moose' in North America
	common deer of temperate Europe and Asia
	large North American deer with large much-branched antlers in the male