This may be rather obvious to some people, but I've always found it nifty.

Sammael - Destroyer of Hope
Ishamael - Betrayer of Hope

Thus we can conclude that 'mael' probably means hope in the Old Tongue. It's a nice small little attention to detail played by RJ. It also insinuates that all of the Forsaken have names that can be directly translated.

Therefore with Lanfear, we might be looking at Lan-Fear ... Daughter-Night, if the Old Tingue can be translated so crudely. Of course this means Lan is a Daughter, which is fun to ponder.

I've been searching through Old Tongue quotes in the series looking for hints to decipher potential translations for other Forsaken names. I've come up short so far, but would like to know if anyone else has found anything. The only thing I've found is that Moridin is also found on the Horn of Valere, which is a nice direct translation of Death i.e. The Grave is no bar to my Call.

Osan'gar and Aran'gar are named after left and right handed daggers, so Osan might mean left and Aran might mean right, if those translations were direct. 'gar' might mean blade, or weapon.