Diaphanous cotton batiste shirtwaists, often trimmed with lace and decorated with whitework embroidery were slangily referred to as ‘pneumonia blouses’ as early as 1905. The pneumonia term is often erroneously thought to date back to the Spanish Influenza of 1918/19, but in fact, the term was falling from use around that time possibly because the term was no longer amusing in light of the severity of the Spanish Influenza.
The term shows up in the 1906 novel ‘A Waif’s Progress’, by Rhoda Broughton, the heroine gets a bad cold “The result of a pneumonia blouse, I suppose! As long as girls strip themselves naked in January they cannot be surprised at their chests and lungs resenting it.”
That same year an article appeared in the New Zealand newspaper The Evening Post referring to a backlash that had started the year before in the U.S. against the style that Americans were calling the ‘peekaboo waist’: