This is from a webpage :
According to Harper Lee’s novel, To Kill a Mockingbird, courage is trying your hardest even if you know you have no chance of succeeding, making the right choice despite the potential consequences, and facing your fears.
I wonder what part of speech 'hardest' is here.
There's at least two perspectives on this.
According to the ESL teaching world, "hardest" must be a noun because of the possessive adjective ("your") before it, which is always followed by a noun.
Also, the structure [ possessive adjective + superlative ] can take many noun phrase roles:
Your best just isn't good enough. (subject)
Do your worst. (direct object)
I went from my fastest to my slowest. (object of preposition)
The other perspective is from academic Linguistics, which I know less about, but you can find an expert opinion here.