Türkische aussprache päş
Etymologie [ 'päsh ] (adjective.) 1918. Unknown; popularly believed to be an acronym for "port out, starboard home", describing the cabins given to upper-class passengers travelling with the Peninsular and Oriental Steam Navigation Company from Britain to India and back. The company denies this practice, despite christening its loyalty scheme the "P.O.S.H. Club" after the myth (the club has since been renamed "Portunus"). A more likely origin is the Romany word posh meaning "half-", as in posh-kooroona meaning "half a crown" - a once-substantial sum of money, and hence by association anything pricey or upper-class. Alternatively posh may have first become a general term for money, after posh-houri, half-penny.
See for other theories. A period slang dictionary defines "POSH" as a term used by thieves for "Money : generic, but specifically, a halfpenny or other small coin."Slang and its Analogues Past and Present: Vol. V, John S. Farmer and W.E. Henley (eds), London (1902), p. 261. An example is given from Page's Eavesdropper, 1888: "They used such funny terms: 'brads,' and 'dibbs,' and 'mopusses,' and 'POSH' ... at last it was borne in upon me that they were talking about money." It is noteworthy that POSH is spelled in capital letters, like the alleged acronym.