Posh
early 20th century: perhaps from slang posh, denoting either a dandy or a coin of small value. There is no evidence to support the folk etymology that posh is formed from the initials of port out starboard home (referring to the more comfortable accommodation, out of the heat of the sun, on ships between England and India).
wiktionary
Unknown.
Most likely derived from Romani posh(“half”), either because posh-kooroona(“half a crown”) (originally a substantial sum of money) was used metaphorically for anything pricey or upper-class, or because posh-houri(“half-penny”) became a general term for money.
A period slang dictionary defines "posh" as a term used by thieves for "money : generic, but specifically, a halfpenny or other small coin". [1] 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."
Evidence exists for a slang sense from the 1890s meaning dandy, which is quite possibly related. [2]
A popular folk etymology holds that the term is an acronym for "port out, starboard home", [3] describing the cooler, north-facing cabins taken by the most aristocratic or rich passengers travelling from Britain to India and back. However, there is no evidence for this claim. [4]
See also the articles mentioned in the References section below for additional discussion.
etymonline
posh (adj.)
by 1914 (1903 as push), a word of uncertain origin, but there is 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); as per OED, see objections outlined in G. Chowdharay-Best in Mariner's Mirror, January 1971; also see here. The acronym story dates from 1955.
More likely it is from slang posh "a dandy" (1890), from thieves' slang meaning "money" (1830), originally "coin of small value, halfpenny," possibly from Romany posh "half" [Barnhart].
The cavalryman, far more than the infantryman, makes a point of wearing "posh" clothing on every possible occasion — "posh" being a term used to designate superior clothing, or articles of attire other than those issued by and strictly conforming to the regulations. [E. Charles Vivian, "The British Army From Within," London, 1914]
