narrowing vs bottleneck

narrowing and bottleneck both are nouns.

Word	Noun	Adjective	Verb	Adverb
narrowing	Yes	Yes	No	No
bottleneck	Yes	No	Yes	No

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

Other hyponyms of narrowing include coarctation, taper, chokepoint, constriction.

narrowing (noun)	bottleneck (noun)
the act of making something narrower	the narrow part of a bottle near the top
an instance of becoming narrow	a narrowing that reduces the flow through a channel
a decrease in width

narrowing (adjective)	bottleneck (adjective)
(of circumstances) tending to constrict freedom
becoming gradually narrower

narrowing (verb)	bottleneck (verb)
	become narrow, like a bottleneck
	slow down or impede by creating an obstruction