The Collaborative International Dictionary of English v.0.48:

Mab \Mab\ (m[a^]b), prop. n. [Cf. W. mad a male child, a boy.]
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   1. A slattern. [Prov. Eng.]
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   2. [capitalized] The name of a female fairy, esp. the queen
      of the fairies; and hence, sometimes, any fairy. --Shak.
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