Described by Stow as a "bourne that sometimes ranne downe Oldbourn hill." But there does not seem to be any authority for this statement, as to a burn or brook running down and giving its name to Holborn Hill.
The name Holborn appears in Domesday as "Holeburne," i.e. the "brook in the hollow" from A.S. "hol" = "hollow," and was probably applied to the rivulet which entered the Thames as the Fleet, or rather to the northern portion of it which flowed through the neighbourhood of Clerkenwell.
In the register of Clerkenwell nunnery Cott. Faust. B. ii. the lands of the nunnery are described as lying "juxta Holeburne in ripam Holeburne," while the garden of the hospitallers is "super Holeburne," indicating that the stream came down north and west from Clerkenwell to Holborn Bridge and not in an easterly direction down Holborn Hill.
The form "Oldbourne" is one of Stow's gratuitous guesses, and rests on no authority whatever. Unfortunately he persisted in spelling the word throughout his work in accordance with his fancied etymology, instead of in the usual manner, with the result that his derivation of the word has, in the past, been very generally accepted.
In later times this northern portion of the Fleet is referred to as Turnmill Brook (q.v.).