The Brent is a river within Greater London

Greater London

Greater London is the top-level administrative division of England covering London. It was created in 1965 and spans the City of London, including Middle Temple and Inner Temple, and the 32 London boroughs. This territory is coterminate with the London Government Office Region and the London...

 which is a tributary of the River Thames

River Thames

The River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...

. It is 17.9 miles (29 km) long, running north-east to south-west, and it joins the Thames on the Tideway

Tideway

The Tideway is a name given to the part of the River Thames in England that is subject to tides. This stretch of water is downstream from Teddington Lock and is just under long...

 at Brentford

Brentford

Brentford is a suburban town in west London, England, and part of the London Borough of Hounslow. It is located at the confluence of the River Thames and the River Brent, west-southwest of Charing Cross. Its former ceremonial county was Middlesex.-Toponymy:...

, Hounslow

London Borough of Hounslow

-Political composition:Since the borough was formed it has been controlled by the Labour Party on all but two occasions. In 1968 the Conservatives formed a majority for the first and last time to date until they lost control to Labour in 1971. Labour subsequently lost control of the council in the...

.
The name is Old English, from Celtic words meaning "holy one" or specifically the linguistic root of the Celtic tutelary goddess

Triple Goddess

The Triple Goddess is the subject of much of the writing of Robert Graves, and has been adopted by some neopagans as one of their primary deities. The term triple goddess is sometimes used outside of Neopaganism to refer to historical goddess triads and single goddesses of three forms or aspects...

 Brigant. A letter from the Bishop of London in AD 705 suggesting a meeting at Breguntford now Brentford

Brentford

Brentford is a suburban town in west London, England, and part of the London Borough of Hounslow. It is located at the confluence of the River Thames and the River Brent, west-southwest of Charing Cross. Its former ceremonial county was Middlesex.-Toponymy:...

, is the earliest record of this place and probably therefore that of the river.
The River Thames can first be identified as a discrete drainage line as early as 58 million years ago, in the Thanetian

Thanetian

The Thanetian is, in the ICS' Geologic timescale, the latest age or uppermost stratigraphic stage of the Paleocene Epoch or series. It spans the time between and . The Thanetian is preceded by the Selandian age and followed by the Ypresian age...

 stage of the late Palaeocene epoch.