hillock vs kopje

hillock and kopje both are nouns.

Word	Noun	Adjective	Verb	Adverb
hillock	Yes	No	No	No
kopje	Yes	No	No	No

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

Other hyponyms of hillock include anthill, formicary, koppie, molehill.

hillock (noun)	kopje (noun)
a small natural hill	a small hill rising up from the African veld