escape wheel

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The rotating notched wheel periodically engaged and disengaged by the anchor in an escapement.

from The Century Dictionary.

• noun The last wheel in the mechanism in clock- and watch-work by which the power of spring or weight is released or allowed to escape, by the catch and release of detent elements controlled by the timed swing of the pendulum or the oscillation of the balance-wheel.

from the GNU version of the Collaborative International Dictionary of English.

• noun The rotating wheel in an escapement mechanism which has notches that are periodically engaged and disengaged by the anchor.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun gear that engages a rocking lever