'Romford' means the wide or spacious ford.
It is first recorded in 1177 as Romfort, from Old English rūm, wide or spacious, and ford. The ford most likely carried the London to Colchester road over the river. But the river was not yet the Rom: in the 13th century it was le Markediche, the boundary ditch, and 'Rom' is a back-formation from the town's name. Downstream it is called the Beam.