The feeling expressed by the noun today is not especially strong - things "take our fancy", or "tickle our fancy". This sense of "whim" was available in Shakespeare's time - Don Pedro says of Benedick "a fancy that he hath to strange disguises" (Much Ado About Nothing, III.ii.30) - but more usually, when talking about the emotions, the word referred to a much more profound feeling of love or even infatuation. Five lines later, Don Pedro says Benedick "is no fool for fancy", which would be confusing if we did not appreciate that here the word means "love". And similarly, when Silvius tells Phebe of "the power of fancy" (As You Like It, III.v.29), or Demetrius talks of "Fair Helena in fancy following me" (A Midsummer Night's Dream, IV.i.162), or Orsino describes Viola as "his fancy's queen" (Twelfth Night, V.i.385), they are all saying much more than simply "I fancy her".
David Crystal is author, with Ben Crystal, of Shakespeare's Words published by Penguin