Here's how it's thought to have happened:
* P&O Steamships: The P&O line was known for its luxurious and expensive voyages, particularly on routes to India and the Far East.
* "Port Out, Starboard Home": Passengers booking first-class tickets on the P&O ships would often request cabins on the "port" side of the ship on the outward journey (to India) and the "starboard" side on the homeward journey (from India). This was because the port side offered the best views during the outward voyage, while the starboard side was preferred on the return journey.
* Code Word "POSH": To streamline the booking process, travel agents developed a shorthand code for these preferences, using the acronym "POSH" - Port Out Starboard Home.
* Evolution of Meaning: Over time, the word "posh" came to be associated with the luxurious and high-class nature of P&O voyages and the passengers who traveled on them. It eventually became a general term for anything elegant, stylish, or upper-class.
It's important to note: This is the most widely accepted theory for the origin of "posh." However, there are alternative theories that suggest the word might have come from another source, such as a slang term for a particular type of garment. Nevertheless, the P&O connection is the most popular and plausible explanation.