sweat vs swelter

sweat is a noun but swelter is not a noun.

Word	Noun	Adjective	Verb	Adverb
sweat	Yes	No	Yes	No
swelter	No	No	Yes	No

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

sweat (noun)	swelter (noun)
use of physical or mental energy; hard work
salty fluid secreted by sweat glands
condensation of moisture on a cold surface
agitation resulting from active worry

sweat (verb)	swelter (verb)
excrete perspiration through the pores in the skin	suffer from intense heat
	be uncomfortably hot