Declan, I don't believe an ironclad case for Aine/Aithne and Eithne/Enya names being different names, can honestly be made. While there are some pronounciation variations by dialect (as I pointed out), the linguistic proof that these are, without question, two different names, isn't very strong.

I look to how the names are used today. As you pointed out, the Donegal pronounciation of the names is virtually identical. I have encountered some people in Donegal who believe they are, in fact, different names, and others who believe it is more likely they are the same names, which have grown different spellings (and hence, in some regions, different pronounciations) down through the centuries.

There is no end to the amount of misinformation out there on the "meaning" of a name. My understanding of this female name, is that all it's derivatives in Gaelic, are in fact derivatives of the extremely broad use of the name in Indo-European cultures, from Ireland to India. So perhaps we just need to agree to disagree.

BTW, the online source for Gaelic names that I use (it is the best I've found, which actually isn't saying much, as most Gaelic name websites are crap) is this one:

http://www.behindthename.com/nmc/iri.html

It offers the following derivations:

EDNA (1)   f   Irish, Scottish
Pronounced: ED-na
Anglicized form of EITHNE

EITHNE   f   Irish, Scottish
Pronounced: EN-ya, EN-a
Means "kernel" in Gaelic.

ENA   f   Irish
Anglicized form of EITHNE

ENYA   f   Irish
Pronounced: EN-ya
Anglicized form of EITHNE

ETHNA   f   Irish
Anglicized form of EITHNE

ETHNE   f   Irish
Variant of EITHNE

ETNA   f   Irish
Anglicized form of EITHNE

ÁINE   f   Irish
Means "radiance" in Gaelic.

AITHNE   f   Irish
Variant of EITHNE