Is the Word Sweltering an Adjective?

SWELTERING (adjective) definition and synonyms | Macmillan Dictionary.

Is sweltering a verb or adjective?

Those are just the adjectives. “Sweltering” can also be an adverb, or a noun (though, if you want to be technical, “sweltering” as a noun is really a gerund, which is a verb pretending to be a noun). Of all the ways to say that it's oppressively hot, “sweltering” or its other forms are among the most popular.

Is Swelteringly a word?

swel·ter. To suffer from oppressive heat.