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In technical literature as well as aircraft user interfaces where there is not enough space to write the whole word, the prefix "trans" is shortened to "x".

Transmit -> Xmit
Transfer -> Xfer

I am interested to know what is the origin of this. I am curious because "Ex" and "Trans" do not have a similar sound.

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4 Answers 4

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X is commonly used to refer to cross because of its shape of two lines crossing.

Trans- means cross/across. Trans- and cross- are interchangeable in many cases.

From Wikipedia (emphasis mine):

In abbreviations, it can represent trans- (e.g. XMIT for 'transmit', XFER for 'transfer'), cross- (e.g. X-ing for 'crossing', XREF for 'cross-reference'), Christ- as shorthand for the labarum (e.g. Xmas for 'Christmas', Xian for 'Christian'), the crys- in 'crystal' (XTAL), or various words starting with ex- (e.g. XL for 'extra large', XOR for 'exclusive-or').

Example: a transatlantic flight is one that crosses the Atlantic, and something that is transdermal crosses through the skin.

The trans- in transmit and transfer is analogous to transatlantic.

Crossing a mit or a fer makes perfect sense.

  • -Mit is from the Latin mittere which means to send.
  • -Fer is from the Latin ferre which means to bear or carry.

'Transmit' often means to send across something or over a specific medium and 'transfer' can be to carry across from one to another.

Therefore trans- is often replaced with X- in certain words.

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  • 2
    to add to the confusion, in electronics XTAL is the schematic designation for (quartz) crystals. crossing, christmas, crystal, X fits it all...
    – dlatikay
    Jul 19, 2020 at 18:22
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    @dlatikay X in "Christmas" comes from an entirely different derivation, Greek chi. Jul 20, 2020 at 3:05
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    I think saying it "is fine and doesn't change the meaning" is a weird description - very few people will read the abbreviation "xfer" and think "ah, yes, a cunning pun with a symbolic cross and the Latin root ferre, this is clearly a word meaning carry across". Rather, they will read it as a conventional abbreviation for English words, and the connection of the prefix trans- to "cross" explains the origin of that convention.
    – IMSoP
    Jul 20, 2020 at 10:12
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    @DavidR The X in Christmas is from Χριστός; the similarity to a cross is coincidental but probably widely used symbolically. Jul 20, 2020 at 13:45
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    @dlatikay The suffix -x in TX (transmitter), RX (receiver), WX (weather), DX ((long-)distance), etc. (as well as XMIT and XTAL) were popularized as abbreviations in the days of Morse code, when radio operators (especially amateurs) discussed technical matters and wanted to keep messages as short as possible.
    – DavidR
    Jul 20, 2020 at 13:51
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In addition to the other edifying answers and comments: from an information-theory viewpoint, given the rarity of initial "x" in English words, the presence of it (especially if unpronounceable) is a clear signal that there is something at play slightly out of the ordinary, and it will not be easily mistaken for anything else. That is, information-theory-wise, the chance of misunderstanding is low (more technically/precisely, the error-correction properties of this usage are excellent).

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  • This explanation works both for Xmit and TX abbreviations for "transmit".
    – Steve
    Jul 20, 2020 at 9:27
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    The chance of confusion with something else is low; the chance of misunderstanding without context or prior knowledge is still high.
    – chepner
    Jul 20, 2020 at 13:31
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    @chepner, indeed, but/and the reader previously unacquainted with the usage will know that they are unacquainted with it, as opposed to mistaking it for something else, I'd think. Jul 20, 2020 at 22:20
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Oddly enough, 'Tx' is used to describe 'a transmitter' or 'to transmit something' and is very much relevant in electronics domain. Similarly, 'Rx' describes 'a receiver' or 'to receive something/reception of signal'. Here is a picture which shows Tx and Rx use in electronics:

enter image description here

Picture source

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    This is because a lot of computer nerds have trouble spelling "tarsn".
    – Hot Licks
    Jul 19, 2020 at 17:07
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    This doesn't explain why the prefix “Trans” is shortened to “X”, which is what the original question asked. Jul 19, 2020 at 17:11
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    @KillingTime Yes, the original question has been answered excellently by Decapitated Soul. I just mentioned an additional point that transmit can be shortened to both 'Xmit' and 'Tx'; the latter being relevant in electronics domain. Jul 19, 2020 at 17:21
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    This doesn't answer the question, but it's good to note. You could leave a comment on the question instead.
    – wjandrea
    Jul 19, 2020 at 20:30
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    Combining ideas in this and the accepted answer, RX/TX could be considered as an abbreviation for "Receive aCROSS the wire" and "Transmit aCROSS the wire" (or indeed "... through CROSSed wires" - as shown in your diagram. No idea of actual historical origin, so this is possibly a backronym.
    – Steve
    Jul 20, 2020 at 9:28
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OED:

trans-, prefix

Etymology: The Latin preposition trans, across, to or on the farther side of, beyond, over’, also used in combination, (1) with verbs, (2) adjectives (3) the neames of geographical features and names, etc.

e.g. transcribe, transcript, transcription, tranship, transport, transmarine, transmural, transatlantic,

The shape of the letter X is described as a cross: The letter is formed by one line crossing another:

b. The letter considered with regard to its shape: chiefly attributive and in other combinations. Hence identified with a cross. X's and O's: the game of noughts and crosses. X chair, a chair in which the underframe resembles the letter X in shape; so X-frame (usually attributive).

1976 Country Life 27 May (Suppl.) 486/1 Late 18th century wheel-back armchairs with saddle seats and X-frame legs.

d. [the letter or mark 'X'] Used to mark a location on a map or the like; esp. in X marks the spot and variants.

1918 J. M. Barrie Echoes of War 5 In the rough sketch drawn for to-morrow's press, ‘Street in which the criminal resided’..you will find Mrs. Dowey's home therein marked with a X.

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