Heel-tap

[heel-tap] /ˈhilˌtæp/

noun
1.
a layer of leather, metal, or the like in a shoe heel; a lift.
2.
a small portion of liquor remaining in a glass after drinking or in a bottle after decanting.
3.
dregs, sediment, or residue.
/ˈhiːlˌtæp/
noun
1.
Also called lift. a layer of leather, etc, in the heel of a shoe
2.
a small amount of alcoholic drink left at the bottom of a glass after drinking
n.

also heeltap, 1680s, “one of the bits of leather that are stacked up to make a shoe heel” (see heel (n.1)); meaning “bit of liquor left in a glass or bottle” first recorded 1780s; the exact connection is uncertain unless it be “the last or final part.”

noun

A few drops of liquor left in a glass: drink three martinis, absolutely no heeltaps

[1780+; origin uncertain; a heeltap glass was one without a flat base, so that it could not be set down until entirely empty (such was presumably also a tumbler), and probably so called because the narrow bottom resembled the narrow tap of a shoe heel]