A device used for easing the foot into a shoe WordNet 3.0 & Open English WordNet

A shoehorn or shoe horn is a tool with a short handle that flares into a longer spoon-like head meant to be held against the inside back of a snug-fitting shoe so that a person can slide the heel easily along its basin to the inner sole. Wikipedia

Tool that lets the user put on a shoe more easily Wikidata

A tool designed to help inserting the heel of the foot into a shoe. OmegaWiki

A smooth tool that assists in putting the foot into a shoe, by sliding the heel in after the toe is in place. This reduces discomfort and damage to the back of the shoe. By slipping it into the back of the shoe behind the heel, the user prevents the heel from squashing down the back of the shoe and causing difficulty; instead the heel slides down the smooth shoehorn, which then comes out easily once the foot is in place. Wiktionary