The correct name woulde be Londinium. For referece see http://www.fireflywiki.org/Firefly/Londinium
KAYLEE: I'd sure love to find a brand new compression coil for the steamer.
MAL: And I'd like to be king of all Londinum and wear a shiny hat.
Given this throw-away line in the Serenity Pilot, it would appear the Londinum is a (possibly backwards) planet ruled by a monarchy.
Or it's a fairy-tale reference. Either way.