In the Fen district of East Anglia: a raised silt bank consisting of the bed and levees of a former river or tidal creek, left above the general level of the land by compaction and lowering of the adjacent peat soil following drainage.
Mid 19th century; earliest use found in Thomas Wright. Origin uncertain. Perhaps the reflex of a Middle English compound from road + holm, the silt banks being so called on account of their suitability as thoroughfares, since they are long, narrow, and raised above the ground, and drain easily in relation to the peat fen through which they run. See further R. Coates in Notes & Queries (2005) June 170–2. If so, the first element could show late Middle English or early modern English shortening of open ō before d; compare also rare short-vowel forms at road. As regards the second element, Coates notes that holm frequently occurs in reduced forms in place names especially in coastal areas of Lincolnshire (where it appears as -ham, -am, -um, etc.).