Shim

Shim noun a washer or thin strip of material used to align parts, make them fit, or reduce wear.
“an aluminium shim reduces the diameter so that a standard stem will fit”
Verb wedge (something) or fill up (a space) with a shim.
“display monitors were shimmed up on cardboard”

This is part of the “What are words for?” project. This word scored a six on a three part scale of allusiveness, political oomph and cultural capital (min score 1, max score 3 for each part of the scale).  Lots of words did. This is one I clawed from the slushpile on a whim.