The Oxford Thesaurus An A-Z Dictionary of Synonyms - taper v.

1) narrow (down) , thin, diminish, come or go down: Note how the trousers taper towards the ankles. 2) Often, taper off. diminish, reduce, thin out, wind down, decrease, fade, lessen, peter out, fall off, wane, subside, let up, slacken, die away or down or off or out, decline, slow (down or up) , weaken, abate, ebb, slump, drop (off) , fall (off) , plummet: Sales of ice skates can be expected to taper off during the summer.