IPA: /ˈhiːlˌtæp/
KK: /ˈhiltæp/
A piece added to the heel of a shoe to make it higher, or a small amount of drink left in a glass or container.
After finishing his drink, he noticed a heeltap left at the bottom of the glass.
Heeltap is formed from "heel" (from Old English "hæle", meaning the back part of the foot) and "tap" (from Old English "tæppan", meaning to strike or hit). The word refers to a strike or hit made with the heel.
Think of the 'heel' of your foot striking or hitting something, which is what a heeltap means.
No commonly confused words.