deepness vs extent

deepness and extent both are nouns.

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

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

deepness (noun)	extent (noun)
the quality of being physically deep	the distance or area or volume over which something extends
the extent downward or backward or inward	the point or degree to which something extends
a low pitch that is loud and voluminous
the intellectual ability to penetrate deeply into ideas