Is return an operator or a function?

Question

This is too basic I think, but how do both of these work?

return true;   // 1

and

return (true); // 2

Similar: sizeof, exit

My guess:

    If return was a function, 1 would be erroneous.

    So, return should be a unary operator that can also take in brackets... pretty much like unary minus: -5 and -(5), both are okay.

Is that what it is - a unary operator?