Lostwithiel the Old Cornish Lost Gwydhyel meaning "tail-end of the woodland".
The view from Restormel Castle looking towards the town shows how this may have come to be.
Lostwithiel is a historic borough.The Lostwithiel constituency elected two members to the Unreformed House of Commons, but was disenfranchised by the Reform Act 1832. It remained a municipal borough until the 1960s, when it became a civil parish.
The seal of the borough of Lostwithiel was a shield charged with a castle rising from water between two thistles, in the water two fish, with the legend
"Sigillum burgi de Lostwithyel et Penknight in Cornubia"
Its mayoral regalia includes a silver oar, signifying its former jurisdiction over the River Fowey.