Is by a noun verb or adjective?

Answer 1

No, the word 'by' is an adverb and a preposition.
The word 'by' is an adverb when not followed by a noun or a pronoun.

• We were standing by when the call came.
• The rest of the crop is put by for the cattle.

The word 'by' is a preposition when followed by a noun or a pronoun.

• The line is from a play by Shakespeare.
• We should be there by ten.
• There's a bank right by the theater.

The word 'by' is also an alternate spelling for the interjection 'bye'.

Answer 2

"by" is a preposition. It is used to indicate the agent performing an action in a passive sentence or to show the method or means of doing something.