outthrust vs rock outcrop

outthrust and rock outcrop both are nouns.

Word	Noun	Adjective	Verb	Adverb
outthrust	Yes	No	No	No
rock outcrop	Yes	No	No	No

As nouns, rock outcrop is a hypernym of outthrust; that is, rock outcrop is a word with a broader meaning than outthrust:

outthrust: an outcropping of rock that extends outward
rock outcrop: the part of a rock formation that appears above the surface of the surrounding land

Other hypernyms of outthrust include outcrop, outcropping.

outthrust (noun)	rock outcrop (noun)
an outcropping of rock that extends outward	the part of a rock formation that appears above the surface of the surrounding land