slip-motion

from The Century Dictionary.

• noun In machinery: An intentional looseness of fit, which allows one part to move without driving the other during a part of the phase of such first part: used in direct-acting pumps where the valve of one is driven by the piston of the other.
• noun A motion of one part on another where only the components in one direction are to be used, as of a pin driving a rocking arm by contact with the sides of the slot in such an arm, or the driving of a Corliss valve-arm by a detent which slips by on the return stroke.