What is the origin of the term "pax"? Pax in commercial transport is used as something like persons or passengers, in the context of counting people, e.g. 150 pax onboard.


(Amadeus capture, source)

I observed that in German writers tend to use the meaning:


  PAX = Persons approximately.
  (Source: European Union and the Committee of the Regions)


English.SE has a page for What does “pax” mean in the context of the apartment rental? Selected answer:


  Pax isn't exactly shorthand for Passengers. It's short for
  Passengers and Passes.  


But the author of the answer agreed that another answer was likely more accurate. The latter has a reference to a magazine, Air Facts: The Magazine for Pilots - 1946:


  Cargo is known as "cargo", but passengers are called "pax" by the
  traffic department, who puts them on and takes them off the airplane
  and "bodies" by the crews who fly them.


Pax could be from passenger as usually assumed in the Aviation community, albeit I don't see why not *pass" instead. I wouldn't be surprised it comes from the merchant navy.

Can we track the use further back to the origin in aviation field?
The 'x' suffix is aviation speak in an abbreviated word called a contraction.  You can think of the 'x' as &quot;cut short&quot; shorthand.  Some are defined in manuals or advisory circulars.  For example, WX is weather as defined in an old advisory circular, AC00-45.
Official or not, a few others that come to mind are:

MX - maintenance
CX - cancel
TX - transmit
RX - receive

Maybe others will chime in the comments with more lore. The -x is also used outside of aviation, and is a common abbreviation marker, e.g. Dx (&quot;diagnosis&quot;), elex (&quot;election&quot;), and Hx (&quot;history&quot;).