Pai means leg or foot in Persian; jama means garment. Paijama were the loose trousers tied at the waist worn across Persia, the Ottoman world, and South Asia, by both sexes, as daywear. The British in India adopted the garment for lounging and sleeping, and the word entered English in the early 1800s as pyjamas or pajamas, the s arriving with the plural trouser logic of pants.
The Raj took the garment and inverted its formality: what was respectable street dress in Isfahan and Delhi became private undress in London. Europe had slept in shirts and shifts for centuries; the pajama arrived as exotic comfort and domesticated within a generation. The two-piece pajama suit is a colonial remix, the South Asian kurta-pajama re-cut for the armchair.
The claim: imperial language absorbs the vocabulary of comfort from the ruled, pajamas, veranda, bungalow, shampoo, because domination is work but leisure is borrowed; the empire's off-duty hours are dressed in the vocabulary of the colonized. Verdict: the Hobson-Jobson lexicon is substantially this list. The words that came home with the troops were not the words of command but the words of rest. Make of that what the pajama-wearing public already did.
How did a Persian trouser word become global bedtime vocabulary?