Sloothby, in the Calcewath Wapentake of Lincolnshire, is a complicated name. There are multiple possibilities for the first element of the place-name. The second element is the Old Norse element by ‘a farmstead, a village’.

One suggestion is that the first element is the Old Norse byname Slóði ‘the lazy one’; however, this name is not found independently in Lincolnshire and is uncommon in Scandinavia. 

Another alternative is that the first element could be slóði used as a river-name, referring to a slow-moving sluggish stream. Sloothby is in the fens and a stream runs by.

Furthermore, the first element could be the Old Norse element slóð ‘a track, trail’, perhaps referring to a track through the fens. 

Sloothby is a joint parish with Willoughby.