The Collaborative International Dictionary of English v.0.48:

Tapadera \Tap`a*de"ra\, Tapadero \Tap`a*de"ro\, n.] [Also
   tapidero.] [Sp. tapadera lid, cover.]
   One of the leather hoods which cover the stirrups of a
   Mexican saddle.
   [Webster 1913 Suppl.]