What is the derivation of posh?

Answer 1

From the Related Link: ; posh : 1918, of uncertain origin; no evidence for the common derivation from an acronym of port outward, starboard home, supposedly the shipboard accommodations of wealthy British traveling to India on the P & O Lines (to keep their cabins out of the sun); see objections outlined in G. Chowdharay-Best, "Mariner's Mirror," Jan. 1971. More likely from slang posh "a dandy" (1890), from thieves' slang meaning "money" (1830), originally "coin of small value, halfpenny," possibly from Romany posh "half."

Answer 2

It's not actually known.

The "common" belief is from the ocean faring part of the British Empire where rich people paid to get the cabins on the port side when travelling to India and the starboard cabins on the way home, so as not to get "too" much sun (Which was not on, as a "rich" person wasn't supposed to be "brown" or "tanned").

It's an interesting thought but more than likely an advertising slogan for the Peninsular and Oriental Steam Navigation Company.

Its most likely origination is from the Romani language posh meaning "half-", as in posh-kooroona meaning "half a crown".

It was also used by robbers. The slang for money was POSH.

Where it does originate from is anyones guess.