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Webster 1913 Edition
Tappet
Tap′pet
,Noun.
(Mach.)
A lever or projection moved by some other piece, as a cam, or intended to tap or touch something else, with a view to produce change or regulate motion.
G. Francis.
Tappet motion
, a valve motion worked by tappets from a reciprocating part, without an eccentric or cam, – used in steam pumps, etc.