The term 'bat of an eye' is a phrase that refers to something happening very quickly, almost instantaneously. The crossword solutions for this term are WINK (4 letters) and IRIS (4 letters). A WINK is a facial expression made by closing one eye briefly, and an IRIS is the colored part of the eye. Both of these words refer to parts of the eye, and together they illustrate how quickly something can happen - in the blink of an eye, or the bat of an eye.