will-o’-the-wisp
noun/ˌwɪl ə ðə ˈwɪsp/
/ˌwɪl ə ðə ˈwɪsp/
[usually singular]- a thing that is impossible to obtain; a person that you cannot depend on
- a blue light that is sometimes seen at night on soft, wet ground and is caused by natural gases burning
Word Originearly 17th cent.: originally as Will with the wisp, the sense of wisp being ‘handful of (lighted) hay’.
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will-o’-the-wisp