I said X usually represents the unknown,key word usually- not always.example Malcom X. Also the most basic algebra-middle school level- starts representing unknown with x. In the case of xmitter, it is short for trans, that is another common use of X, replacing trans, cross or across. example RR Xing, Xatlantic flight, Xgender, I have seen all of these used and more.

The parrot was sitting on Steve's shoulder.

We must punish this apostate priest.

[H]e has all along (by his threatening and unpolite behaviour to my friends, and whenever he speaks of them) given me reason to conclude, that there is more malice to them, than regard to me, in his perseverance.