No, the word 'briefly' is an adverb, a word that modifies a verb. Example sentence:
We briefly stopped at the library to return some books.
No, briefly is an adjective.
The word "briefly" is not a noun. It is an adverb. A related abstract noun is brevity (briefness). An example of an abstract noun is the word "freedom" because abstract nouns are not something physical like a place or a person, but an idea like freedom or justice or happiness.
Brevity as a noun has the adverb form brief, and the adverb form "briefly."
Verb Refer to something briefly and without going into detail. Noun A reference to someone or something.
more briefly, most briefly
briefly
more briefly
Yes, most commonly is used as a verb. It is means to "see briefly". It can be used occasionally as a noun, as in "I caught a glimpse of something off in the corner."
The noun duration has an adjective form, durational, but not an adverb form.---Adverbs of duration are adverbs of time, including briefly, constantly, incessantly, and continuously.
Briefly is the correct spelling.
Briefly is an adverb.
You would say "Jack and Jill talked briefly."