Hinge

The hook with its eye, or the joint, on which a door, gate, lid, etc., turns or swings; a flexible piece, as a strip of leather, which serves as a joint to turn on.

That on which anything turns or depends; a governing principle; a cardinal point or rule; as, this argument was the hinge on which the question turned.

One of the four cardinal points, east, west, north, or south.

To attach by, or furnish with, hinges.

To bend.

To stand, depend, hang, or turn, as on a hinge; to depend chiefly for a result or decision or for force and validity; -- usually with on or upon; as, the argument hinges on this point.

a circumstance upon which subsequent events depend; "his absence is the hinge of our plan"