HEEL, (i) (O. Eng. hela, cf. Dutch hid; a derivative of O. Eng. hoh, hough, hock), that part of the foot in man which is situated below and behind the ankle; by analogy, the calcaneal part of the tarsus in other vertebrates. The heel proper in digitigrades and ungulates is raised off the ground and is commonly known as the "knee" or "hock," while the term "heel" is applied to the hind hoofs. (2) (A variant of the earlier hield; cf. Dutch hellen, for helderi), to turn over to one side, especially of a ship. It is this word probably, in the sense of " tip-up," used particularly of the tilting or tipping of a cask or barrel of liquor, that explains the origin of the expression " no heel-taps," a direction to the drinkers of a toast to drain their glasses and leave no dregs remaining. " Tap " is a common word for liquor, and a cask is said to be " heeled " when it is tipped and only dregs or muddy liquor are left. This suits the actual sense of the phrase better than the explanations which connect it with tapping the " heel " or bottom of the glass (see Notes and Queries, 4th series, vols. xi.-xii., and sth series, vol. i.).
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)