from The Century Dictionary and Cyclopedia
- n. In Paris, a closed telegraph card sent by pneumatic tube to various central stations in the city and delivered by telegraph messenger. It is of a blue color, doubled in the middle and sealed on three sides by means of its prepared mucilage-covered edges.
Sorry, no etymologies found.
Bruxelles, went to the Hôtel Dominici, near the Place Vendôme, sent you a _petit-bleu_, and arrived here at 6.30.