Wow, it's awesome that you're taking the time to do something so in-depth! Though, wouldn't it be more of an encyclopedia than a dictionary?
Anyway,
1)Roonwit the centaur-At the beginning of LB, he told Tirian about how the stars didn't say anything about Aslan coming, and how the stars were in really "disastrous conjunctions". Then Tirian sent him as a messenger to Cair Paravel so that they could send in reinforcements. He got killed by a Calormene arrow near the end of LB.
Griffle the dwarf-He was the leader of the group of dwarves in LB that Tirian&Co. rescue from two Calormene soldiers (he doesn't join the group because he doesn't believe in Aslan anymore)
Sorry there's only two and they're both people and not words.
2)I can't really think of anything, although the only book that I've currently got with me is The Last Battle, which explains why all my suggestions are from that book.

You know I think you're right about Adela being the first term, I reallr could not come up with anyting before that. Cool idea by the way.
Since my mind is stuck on A's now, haha, here are a couple that may be easy to miss:
Azaroth, Calormene goddess
Alambil, the planet seen from Narnia, "Lady of Peace"

Mrs. Pevensie, Mother of Peter, Susan, Edmund, and Lucy

You know I think you're right about Adela being the first term, I reallr could not come up with anyting before that. Cool idea by the way.
Since my mind is stuck on A's now, haha, here are a couple that may be easy to miss:
Azaroth, Calormene goddess
Alambil, the planet seen from Narnia, "Lady of Peace"

ZohMiGosh!!!!!!! How did you find out about the Calormene Goddess?!?! I don't remmeber there being a Goddess mentioned in the books! Although that might be just me- I have a nagging feeling it's when Aravis goes off to worship some Goddess or other when she's actually going to try and kill herself before Hwin stops her, Darn me and my forgetfulness

Nope, that goddess is Zardeena. She is the goddess of the night, as well as the goddess of maidens in preparation of marriage.

Centaur said:

My first term alphabetically is Adela Pennyfeather (a student in Experiment House, member of Them). Just wondering if anyone can think of a term that comes before that.

Adela Pennyfeather should be listed under P., surely.
Anyway, since boys are called “Sons of Adam” throughout the Chronicles I suggest that Adam should precede Adela. Not everyone who reads Lewis is a Christian, and even Christians may not fully understand the reference.