'Ruislip' is thought to mean the leaping place where rushes grow.
It appears in the Domesday Book of 1086 as Rislepe, from Old English rysc, rush, and hlȳp, leap. The leap is thought to have been a spot where the River Pinn was narrow enough to jump across; the village probably grew up south of a crossing place on the Pinn. The river itself was once also known as Ruislip Brook.