A is for the Archanis system, officially disputed between the Federation and the Klingon Empire until the Khitomer Accords of 2293.
B is for bottomless shafts. Should never exist on a starship. Regardless of how big it is.
C is for the Ceti eel, one of the only surviving lifeforms on planet Ceti Alpha V after the planet's ecosystem was laid waste.
D is for Dark-matter nebulas.
E is for the Enterprise XCV-330, the first warp-powered human spacecraft to bear the name and in service many years before the much more advanced Enterprise commanded by Captain Jonathan Archer.
F is for Federation Funny Farm.
G is for Gary Mitchell's friendship with James T. Kirk, which lasted fifteen years.
H is for Harcourt Fenton Mudd.
I is for Ilia's Oath of Celibacy before coming aboard the newly refitted Enterprise.