history - Why is "x" used as an abbreviation for some nouns?

This question is related, but is not a duplicate, of Why do some words have "X" as a substitute?.

I have noticed that a few nouns can be significantly abbreviated with an "x" at the end. Some examples come to mind:

• Transmit → Tx


• Receive → Rx


• Passengers → Pax


• Tickets → Tix

There are likely others in existence I'm not aware of. Most abbreviated nouns ending in "x" seem to be used only as technical jargon (in this case, Fax, Fax, Transportation, Entertainment, respectively). What is the history of using "x" at the end of a word to severely shorten it? And, does the usage of "x" in this context have a single word to describe it?