A reference to the nearby river which was first recorded as Randesbourne in 1360. How the river got its name is uncertain but one suggestion is that it was after a medieval landowner named Rendel. Others say that the Raven reference is of relatively late origin and so is unlikely to refer to the breed of bird. But if the name is Saxon other possible meanings are the fast-flowing stream or the crusted stream, referring to algae-covered or stagnant water. Perhaps the most romantic suggestion was given in Charles Knight’s 1842 history The Journey-Book of Kent. In it he writes: “The history or tradition of the origin of the Ravensbourne ‘When Caesar was encamped here, his troops were in great need of water, and none could be found in the vicinity. Observing however that a raven frequently alighted near the camp, and conjecturing that it was for the purpose of quenching its thirst, he ordered the coming of the bird to be watched for, and the spot to be particularly noted. This was done, and the result was as he anticipated. The object of the raven’s resort was this little spring; from thence Caesar derived a supply of water for the Roman legions; and from the circumstance of its discovery, the spring was called the Raven’s bourne or brook’.
“The water was formerly in great repute for its medicinal virtues, and was used to bathe in. Till about the commencement of the present century there was a bathing-house, overhung with some very beautiful trees. The spring and the heath then formed the great objects of attraction to the gentry and other residents of the neighbourhood for some miles round: on a bright summer day Keston Common (as the heath is called) might often be seen dotted, as it were, with parties of people, the gay costume of the ladies contrasted upon the brown heath, and the air ringing with the sounds of laughter and music. The crystal waters of the Ravensbourne now rise into the circular basin, through small holes with which its bottom is entirely pierced: from the basin they flow through an opening near its top into a concealed trough, and then into the first of the ponds. It never stops, never dries up; it flows to-day as it flowed two thousand years ago, when the Roman saw it bubbling up almost concealed in the brown heath.”
David Mills in A Dictionary of London Place Names takes a more prosaic view, suggesting that the earliest spellings which also include Rendesburne (1372) and Randysborne (1516) offer a clue to the naming of the river, it probably means “boundary stream, from Old English rand, *rend and burna. The later spelling is thus due to folk etymology. In its 10-mile course, the Ravensbourne forms the boundary between several sets of parishes.”