E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The fairies midwifei.e. employed by the fairies as midwife of dreams (to deliver mans brain of dreams). Thus when Romeo says, I dreamed a dream to-night, Mercutio replies, Oh, then, I see Queen Mab hath been with you. Sir Walter Scott follows in the same track: I have a friend who is peculiarly favoured with the visits of Queen Mab, meaning with dreams (The Antiquary). When Mab is called queen, it does not mean sovereign, for Titania was Oberons wife, but simply female; both midwives and monthly nurses were anciently called queens or queans. Quén or cwén in Saxon means neither more nor less than woman; so elf-queen, and the Danish ellequinde, mean female elf, and not queen of the elves. Excellent descriptions of Mistress Mab are given by Shakespeare (Romeo and Juliet, i. 4), by Ben Jonson, by Herrick, and by Drayton in Nymphidea. (Mab, Welsh, a baby.)