elk vs hart

elk and hart both are nouns.

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

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

Other hyponyms of elk include stag, hind, brocket.

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