To insert anything somewhere (especially between other things), such as an affix into a word. (Compare interpolate.)
To insert an extra month into a calendar for the same purpose. The Hebrew calendar has such a month.
To insert a substance between two or more molecules, bases, cells, or tissues.
To insert an extra leap day into a calendar in order to maintain synchrony with natural phenomena.
To force (something) into (a tight space); to squeeze (something) into (a schedule, etc); to exert great effort to insert or include (something); to include (something) despite potent reasons not to.
To use a shoehorn.
To force some current event into alignment with some (usually unconnected) agenda, especially when it is fallacious.
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.
Anything by which a transaction is facilitated; a medium.