There are several theories to the placename 'Ainsdale' which today means 'the dale of Ains'.

The Norse Theory
Vikings are known to have settled along this protected part of the coastline and given their names to other villages such as Forniby(Formby) and Kirk (Kirkdale). The 'Ain' part of Ainsdale would relate to the Norse name 'Einulf'. However this name is not reliable.

The Olde English Theory
The name 'Aegenwulf' is the closest English name which could have contributed to the first part of the name.

Viking Raiders
The most likely name to fit with the 10th century settlers is the Old Norse name 'Einbiorn'. As the transition can be seen with the introduction of Norman language and through the evidence in the following documentations:

Einulvesdal,Doomsday Book (1086)
Aynuluisdale, Cockersand Chartulary (1206)
Aynuldale, Lancashire Pipe Rolls (1279)
Aynolfisdale, Chorley Documents (1309)
Aynoluesdale, Lancashire Court Rolls (14??)
Aynolsdale, Cockersand Chartulary (1451)
Ainsdale (1780)