depth vs extent

depth and extent both are nouns.

Word	Noun	Adjective	Verb	Adverb
depth	Yes	No	No	No
extent	Yes	No	No	No

As nouns, extent is a hypernym of depth; that is, extent is a word with a broader meaning than depth:

depth (noun)	extent (noun)
the extent downward or backward or inward	the distance or area or volume over which something extends
degree of psychological or intellectual profundity	the point or degree to which something extends
the attribute or quality of being deep, strong, or intense
the intellectual ability to penetrate deeply into ideas
(usually plural) a low moral state