Etymology of last names?

I'm researching a last name (Echlin) that I believe originated in the north of Scotland (Pittadro area) and the furthest back I've found a reference is 1407, and it was spelled Echlyne.

I found an internet site that referenced an old work:
This site (a interpretation of Scottish place-names) states that:
Echline, 'Radulphus de Echelyn' (Chart. Melr.); Echlinge, 1449 (RMS), is the dative of eachlann, 'a horse enclosure, paddock'; compare Aghlin in Leitrim (Joyce).

I have also found this spelt Aichlinn as a Gaelic form of Echlin as a first name in Ireland.

In addition, searching through a Scots-Gaelic to English dictionary, I found the name Echline was Gaelicized to Eachlainn (very close to Eachlann). There is a Mt. Eachlainn mentioned in one of Turlough O'Carolan's most famous works, Si Beg si Mor.

Now when I posted this to a newsgroup, I got an alternative meaning:
In Dublin, there is a street that starts at the Guiness Brewery, and runs south for a block or so. The sign says (in Gaelic)"Sraid Aislinne", and below, "ECHLIN STREET".
According to the Gramadach Lexicon Gaelic dictionary, and my Irish homelander friends, 'aislinne' is from 'Aisling' which means "DREAM, or TO DREAM".

I'm fairly convinced the (family) name is Scottish in origin, but I'd like to know the meaning, and the family DID move to ireland in the 1500's or so. But well, I'm at a bit of a loss. Echlyne, Echelyn, Echline, Echlinge, Eachlainn, Eachlann, Echlin, Aichlinn, Aislinne... how do I know what's just a sound-alike and what's connected linguistically? I mean we all know spelling way back when was arbitrary, but really, this is ridiculous. Who's right? The irish or the Scottish? Are there similar-sounding names in both languages that mean entirely different things (paddock vs. dreamer?) I'm more inclined to believe a last name means something prosaic myself.

In short, help!