A device worn in a shoe or boot to make the wearer look taller or to correct a shortened leg WordNet 3.0 & Open English WordNet

A removable shoe insert, otherwise known as a foot orthosis, insole or inner sole accomplishes many purposes, including daily wear comfort, height enhancement, plantar fasciitis treatment, arch support, foot and joint pain relief from arthritis, overuse, injuries, leg length discrepancy, and other causes such as orthopedic correction and athletic performance. Wikipedia

removable sole or form-fitted foot support inside shoes Wikidata

Any device inserted into a shoe to lift the heel of the wearer, for the purpose of making the wearer appear taller, or correcting a limb length discrepancy. Wiktionary

A wedge-shaped shoe insert that can be affixed inside any footwear to make the wearer look taller. Wiktionary