Appropriated Variants
This term is one I think I've created. It is used to designate a form of variant where a name alternates with a seemingly different one. The variant owes its existence to attempts to provide an English translation for a Gaelic surname, resulting in what appears to be an illogical variant.
Many people will be aware that the apparently English surname Smith is frequently found in Co Cavan, and that it is found there because the old name Mac an Ghabhann, a very common Cavan Name, was 'translated' from its original (Son of the Smith). But McGowan has survived as well.
In our studies Gray and Colreavy provide an example of this. The explanation lies with the Gaelic origins of the name. Mac Cathal Riabhaigh (meaning son of Grey Cathal) was the original name. Phonetically this was pronounced Mac-ohal-reev-ig. This was mangled into English as Ma-Col-rave-ee and, with the Mac part removed, eventually it became Colreavy (or Colravy, or even Culravy). Meanwhile somebody who took an interest in the original Gaelic name realised that translated it contained the word "grey" and declared the English surname should therefore be "Gray". There are numerous instances of families using both Colreavy (and its direct variants) and Gray in their dealings.
Other known examples are Benbo, Bimbo and MacNabola; and Keville and Kivelhan (the latter two derived from not-dissimilar sounding but different Gaelic surnames).