Late 19th century; earliest use found in William Locke (1863–1930), novelist. From French PLM, initialism from Paris–Lyon–Méditerranée, the name of a railway company (created in the 1850s).
Definition of PLM in US English:
PLM
noun
Paris–Lyons–Mediterranean (Railway).
Origin
Late 19th century; earliest use found in William Locke (1863–1930), novelist. From French PLM, initialism from Paris–Lyon–Méditerranée, the name of a railway company (created in the 1850s).