In case; if; introducing an alternative clause, followed by a correlative or, or or whether.
Which; properly of two.
I don't know whether I shall know him. – The Burial of the Guns by Thomas Nelson Page
I don't care whether I ever get it or not. – The Mysterious Rider by Zane Grey
" I don't know whether I ought to be nice to you or not, Captain Merrithew," she said. – Dan Merrithew by Lawrence Perry