Wikipedia
A fluid coupling or hydraulic coupling is a hydrodynamic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch. It also has widespread application in marine and industrial machine drives, where variable speed operation and controlled start-up without shock loading of the power transmission system is essential.
Usage examples of "fluid coupling".
The vehicle didn't spin because it was some distance farther from the blast and its tires provided more stability than the fluid coupling of pressurized air linking the combat car to the ground.
Tranter dragged the right skirt, not in error but because the direct friction of steel against gravel was hugely more effective at transferring momentum than a fluid coupling of compressed air.