shim

 
Pronunciation: /ʃɪm/

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 (shims, shimming, shimmed)

[with object]
  • wedge (something) or fill up (a space) with a shim: display monitors were shimmed up on cardboard you may have to shim the tube

Origin:

early 18th century: of unknown origin