X is for XOX, a sentimental favorite cable pattern.
X is for Xena, a recently discovered minor planet officially named Eris or object 2003 UB313. While I have no strong feelings about Pluto's planetary status, I do wish the astronomical authorities had conformed with past practice and honored the name selected by the discoverers of Planet X and its satellite, which they dubbed Gabrielle.
And X is for xylem, which with phloem comprises the wood of trees. Some yarns derived from plants use only phloem, but the fabulously exquisite Habu paper yarns use both.
[ETA 11/29/06: Margene is having a contest for ABC-Alongers who finish – the prize is xocolate!]
See the rest of my ABCs.