Thurnby, in the Gartree Hundred of Leicestershire, probably derives from Old Norse þyrne, þyrnir, þyrni ‘a thorn-bush’ and Old Norse by ‘a farmstead, a village’.
It is also possible that the specific element is the Old Norse byname Þyrnir. However, when taken with the neighbouring parish Bushby these names appear to record an area of former scrubland. This land remained poorly exploited until the period of Scandinavian settlement. Some earlier spellings of the name show substitution of Old English þorn ‘a thorn-tree’ as the first element.
