Sentence:  For some reason, adjusting the 400-day clock <WSD>escapement</WSD> strikes fear into the hearts of many clock repairers. 
Meaning of the word marked with <WSD> tags:  The contrivance in a timepiece (winding wristwatch) which connects the train of wheel work with the pendulum or balance, giving to the latter the impulse by which it is kept in vibration.