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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?

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    Wiktionary has some information and additional examples about "-x" as an abbreviation: en.wiktionary.org/wiki/-x#Suffix_4.
    – geoff
    Commented Mar 8, 2017 at 20:54
  • 6
    Note that X is often used to mean "trans-", as in "Xmit". For "Tix", though, the reason probably is simply the sound similarity.
    – Hot Licks
    Commented Mar 8, 2017 at 21:06
  • X is also used to stand for cross; e.g., LX = lacrosse. There is no special word for abbreviations or initializations ending in X or any other letter AFAIK. It's all part of an inclination to shorten, to leave out what is already known--e.g., here, the OP, ELL. Note that in entertainment FX (not Fax) stands for effects, as in special effects. Also, Rx also means prescription; most acronyms and abbreviations have multiple meanings depending on context.
    – Xanne
    Commented Mar 8, 2017 at 21:47
  • I've always understood pax to stand for (paying) Passengers and (prepaid) Passes in the UK bus industry. In which context the x could be interpreted as a "wildcard" symbol covering both -ssengers and -sses. Commented Mar 8, 2017 at 23:07
  • 1
    I think tickets->tix is a bit different to the other examples because it is a logical abbreviation based on the sound of the letter X being a reasonable substitute for the letters cks. So tickets becomes ticks becomes tix.
    – nnnnnn
    Commented Jul 8, 2021 at 7:12

2 Answers 2

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Telegraph machines couldn’t type dots, so X is the next best thing

The use of X at the end of abbreviations comes from the days of the telegraph, where sending an actual dot (period/full-stop) required more effort than just sending another letter.

TX, RX and PAX all come from telegraphy.

There’s also a strong argument for RX originating from the prescription symbol, (short for the latin “recipere” - “take…”), and although that’s not actually X, but rather a line through the leg of the R, it was often typed as Rx.

… but sometimes X is just phonetic

“Fax” is a phonetic rendering of the first syllable of “facsimile”, tix is a shortening of “tics”, which itself is the plural of tic, short for “ticket”

What’s a telegraph?

A telegraph was originally a five-wire connection that allowed messages to be sent between stations. By placing a voltage on one or more of the wires, a message could be sent nearly instantly over long distances. Later, the telegraph companies came up with clever signalling systems that let them carry the same signals on just one wire, but the original system was five parallel wires. That limit of five “wires” is important, because it created a limitation on what you can send by telegraph.

In order to have the messages make any sense, you need to agree what each combination of on or off lines means, and the system used in the USA and most other countries until the mid-1960s was what is known as International Telegraphic Alphabet No. 2

Letters or figures, but not both

Using five wires with just “on or off” signalling meant that there were only 32 possible combinations, and one of those had to be kept for “nothing is happening right now” (all lines off). But the remaining 31 possible signals are barely enough for all 26 letters of English (let alone other alphabets), and they leave no way of sending numbers or punctuation marks.

To get around this problem, the system gave a unique code for the letters A to Z and the space character, but also defined one of the remain given the meaning “I will now switch to using numbers”. When a receiving station got that code, they would stop looking up the incoming codes on the “letters” page of their code book, and instead used the “figures” list. Sending the “switch” code while in “figures” mode would tell the receiver to interpret the characters as letters again.

Time is money

The cost of a telegraph is fixed: an operator, a printer and a telegraph-line between stations. So, the more you can send along that wire, the more money you can make. This lead to the use of abbreviations for common words, especially longer ones.

So, instead of writing “Transmission” the operator would prefer to just send “T.”, knowing that the receiver would understand the meaning.

But: there’s no period (full-stop) symbol available while the telegraph system is in “letters mode”. So, rather than send “[switch-to-numbers][DOT][switch-back-to-letters]” every time a dot was needed, the operators would use X as a substitute: very few English words end in X, so it was an ideal marker for an abbreviated word. It was two less keystrokes, but importantly it was far faster to send.

Air travel needed fast information

When people began to travel by air, the telegraph became essential. This is where abbreviations like WX (“weather”) and PAX (“passengers”) originated. Both were essential things for airports to know.

From air-travel PAX spread into hotel reservations, and though you can occasionally still see it today on occasion, the hotel people I know consider it to be an affectation.

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The letter "X" has long been used as a place-holder.

It was once standard for illiterate persons to sign legal documents with an "X".

Mathematicians use the letter "x" quite often as a place-holder.

For example, a mathematician might write, "∀ x, y, z ∈ ℝ, (x = y) ⋏ (y =z) ⟹ (x = z)"

It is standard to use an "x" to mean, "replace the x with some other string of symbols".

It is a convention.

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