Can we abort executing an ability after we already are pressing the key for it?

Sorry, if too elemental or the answer is plain no. My second day playing.

Let's say you play Ashe , you press and hold W while you target the Volley with your mouse pointer. Your target hides or moves and you want to abort the shot and try later. If you lift the finger of the key the shot goes off anyway. Is there a way to abort that wasteful shot?

I tried stuff with the mouse, but to no avail. :/

Thanks.