'Posh' never stood for anything at all
The most popular origin story for a word about class turns out to be pure invention, and the truth is far less flattering to the class it describes.
The tidy story goes: on ocean liners between Britain and India, the best cabins were shaded from the sun — port side outbound, starboard side home — and wealthy travelers supposedly got tickets stamped "P.O.S.H." It's a perfect little acronym, cited in a shipping-line song and repeated in etymology corners for a century.
There is no evidence it ever happened. The shipping company, P&O, says it never issued such tickets, and none have surfaced despite decades of collectors hunting for one. The story itself doesn't even appear in print until 1935 — more than two decades after "posh" was already established in English meaning "stylish" or "upper-class." Linguists now trace the acronym explanation to a broader pattern: English speakers love inventing acronym origins for old words, even though acronyms as a naming convention barely existed before the 1930s.
The real root is likely much less romantic — old slang for money, possibly borrowed from Romani, that drifted from meaning "cash" to meaning "someone who has plenty of it" to meaning "expensive-looking."
The fake story survives because it flatters the word it's explaining. The real one just describes what money quietly does to language.