1 used when talking about a choice you have to make or about two different possibilities: He asked me whether she was coming. | The decision whether to see her was mine alone. | whether or not: I coudn't decide whether or not to go to the party.2 used to say that something definitely will or will not happen whatever the situation is: I'm sure we'll see each other again soon whether here or in New York. | whether... or not: Whether you like it or not, you're going to have to face him one day.USAGE NOTE: WHETHER GRAMMAR Whether and if are often used in similar contexts. However, whether is usually used for if when you also use the word or especially at the beginning of a sentence. People say: Whether you see her or not, phone me later. | If you see her, phone me. If can usually be used instead of whether with clauses following some verbs and adjectives: I wonder whether/if she can come. | He wasn't sure whether/if he could come (NOT ...whether could he come). But you use whether (NOT if) before infinitives: The question is whether to go or stay. Whether is also used after prepositions: It depends on whether he's ready or not. It is also used after nouns: It's your decision whether you go or stay. You often use whether with ...or not sentences, for example: You're coming whether you like it or not. | We have to decide whether or not to support this proposal. SPELLING Note the spelling is whether (NOT wether). Wheather (=sunshine, snow etc) is a completely different word.
Longman dictionary of contemporary English. 2004.