WordNet sense 1 (anything that serves by contrast to call attention to another thing's good qualities):

enhancer

WordNet sense 2 (a device consisting of a flat or curved piece (as a metal plate) so that its surface reacts to the water it is passing through):

hydrofoil

WordNet sense 3 (picture consisting of a positive photograph or drawing on a transparent base; viewed with a projector):

transparency

WordNet sense 4 (hinder or prevent (the efforts, plans, or desires) of):

baffle, bilk, cross, frustrate, scotch, spoil, thwart