Various uses of a LINCHPIN, which is a pin inserted into a hole of a twisting pole (axle) to prevent a wheel from sliding off the end of the axle, or used to connect one cart to another in a 'train' configuration resembling copulation, and so on.「Screwing rotations in plugging orifices and cavities with two sets of lips for copulation with young and small children」as something which requires GOVERNING:「…to make and administer the public policy and affairs of a state, for example. Exercise sovereign authority over. To control the speed or magnitude of, regulate. To control the actions or behavior of people. To keep under control. Restrain impulses. To exercise a deciding or determining influence on」
[ https://www.thefreedictionary.com/govern 2014-12-18 ]
In practical terms, the Chinese lords constructed patrolled walls and medical inspection gateways at key points around prostitution and brothel districts in an attempt to GOVERN and CONTROL the spread of infectious disease, the lynchpin of epidemic scourges affecting humanity.
Meaning to GOVERN, to CONTROL, HAVING JURISDICTION OVER some area of responsibility or territory as「revolving potential harm」(reinfection) that must be GOVERNED, KEPT UNDER CONTROL. In English also,「lynch」means「at a right angle」as when hanging from a tree limb in order to MAINTAIN CONTROL over others.
Refers to the LYNCHPIN, a VITAL, WEDGE-SHAPED key item used to lock in place on a shaft at a right angle, without which「potentially great harm」can result due to loss of CONTROL and loss of the wheel, and the goods, and those riding, and the yak, etc. After a lynchpin broke or became loose, the whole load on the wagon was dumped. Having the lynchpins properly set enables MAINTAINING CONTROL. Gateway inspection stations that restricted access by diseased WEDGE-SHAPED PINS were allegorically the LINCHPINS of control over the spread of disease due to a「rotation of screwings among plugging orifices」of the service providers.

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: clamps for crossbar of carriage
Japanese EDRDG: cross bar at end of carriage pole
Unihan extended: the cross-bar at the end of a carriage pole; linchpin of a large carriage