Yes, it is. It is the comparative form of the adjective smart (meaning more intelligent, not more fashionable).
Yes, there has been at least one girl who was smarter than at least one boy.
Cautious IS an adjective. An adjective is an action!
Smart, Smarter, Smartest
smarter, smartest
smarter, smartest
It can be an adverb (much smarter, much more easily), but it can also be an adjective (e.g. much has been said),
smarter
The coyote is smarter
Dumber is the opposite of smarter.
Yes it does make you smarter
A raven seems to be smarter.
they get smarter bye watch the others
The superlative of smarter is "smartest."
Yes, they're actually smarter.
They are smart, but humans are smarter.
No I am smarter than every body.
Smarter (in the sense of cleverer) = Acutulior