a noun
NO!!! 'Circle' can be a verb ' to circle' or a common noun ' the circle'. 'circular' is the adjective.
Adjective.
The word 'engineering' can be used as an adjective, ex: an engineering project.
A verb in the past tense.
No, it is an adjective. Breathe is a verb, breathing is a verb too... but then breathable is an adjective, which makes unbreathable an adjective.
Wet can be used as an adjective. It can also be used as a verb to describe an action.
Brief can be an adjective, a noun or a verb.
It's an adjective.
verb of brave?
Restless is an adjective. Restless is not a verb.
Coincide is a verb. Coincidental is the adjective.
"No" is usually an interjection or an adjective, but never a verb!