(used to introduce the first of two or more alternatives, and sometimes repeated before the second or later alternative, usually with the correlative or): It matters little whether we go or stay. Whether we go or whether we stay, the result is the same.
(used to introduce a single alternative, the other being implied or understood, or some clause or element not involving alternatives): See whether or not she has come. I doubt whether we can do any better.
Archaic. (used to introduce a question presenting alternatives, usually with the correlative or).
which or whichever (of two)?
whether or no, under whatever circumstances; regardless: He threatens to go whether or no.