'Rickmansworth' means the farm or enclosure of a landowner called Ryckmer, or Ricmær.
The ending -worth means a farm or stockade. The Domesday Book of 1086 records the manor as Prichemaresworde, or Prichemareworde in another reading. Later spellings include Rykemarwurthe (1119–46), Rikmansworth (1382) and Rykemerysworth (1418). Locally the town is sometimes shortened to 'Ricky', as in the annual Ricky Week each May.