It's Old English for "Noble Serpent".
I've been using it since the early '80s, originally assembling it from a "Random Old English Name Generator" table in an early issue of Dragon Magazine. If I recall correctly, "Lind" (serpent) was only on the prefix table, not the suffix, so from a gamer standpoint, I "cheated" -- no idea how well or poorly it may work on a grammatical standpoint.
The original "Athelind" was actually a Champions character, a centuries-old dragon who decided to take up superheroing as a lark.* A decade or so later, when "The Boojum Snark" decided that it would be more comfortable for the rest of alt.fan.dragons to address him by a name rather than a title, he adopted it as his nom de guerre.
And the rest is history.
* At almost exactly the same time, a comic called The Southern Knights, and that Atlanta-based superhero team included a centuries-old dragon who also decided to take up the crimefighting trade. Needless to say, my fellow players immediately brought it to my attention.