From The Heretic Knowledge Vault
A rank in the elven military, and probably in others as well. The only significant character yet identified as a Commander is one Nisotta, who's invoked when Sarine, Jon and Sara trek to Praenubilus Astu to try to rescue the Errant-napped Meji, and address the Elven Council. Interestingly, Nisotta seems to play as important a role in the elven bureaucracy as the presumably higher-ranking High Commander Yenhael.
As in real life, a Commander appears to outrank a Lieutenant, at least in the elven scheme of things. Nisotta receives a report from an unnamed elven Lieutenant during the grand melee with the berserk Ian Samael, under conditions that make it clear that the looey is on the battle lines while the Commander is directing the battle from the rear -- as usual. (In Nisotta's defense, she's not nearly as far in the rear as Yenhael, at least.)