extend vs overlap

extend is not a noun while overlap is a noun.

Word	Noun	Adjective	Verb	Adverb
extend	No	No	Yes	No
overlap	Yes	No	Yes	No

As verbs, overlap is a hyponym of extend; that is, overlap is a word with a more specific, narrower meaning than extend:

Other hyponyms of extend include cross, span, sweep, traverse, sweep, overspread, spread, ridge, constellate, dot, stud.

extend (noun)	overlap (noun)
	a flap that lies over another part
	the property of partial coincidence in time
	a representation of common ground between theories or phenomena

extend (verb)	overlap (verb)
extend one's limbs or muscles, or the entire body	extend over and cover a part of
thrust or extend out	coincide partially or wholly
extend in scope or range or area
lengthen in time; cause to be or last longer
continue or extend
expand the influence of
increase in quantity or bulk by adding a cheaper substance
prolong the time allowed for payment of
use to the utmost; exert vigorously or to full capacity
open or straighten out; unbend
extend or stretch out to a greater or the full length
cause to move at full gallop
offer verbally
make available; provide
span an interval of distance, space or time
reach outward in space
stretch out over a distance, space, time, or scope; run or extend between two points or beyond a certain point