[Literally] "third night own servant". He that comes guest-wise to an inn or house, and lies there the third night, after which he is accounted of that family. And if he offend the king's peace, his host was answerable for him.--Thomas Blount's Law Dictionary and Glossary, 1717
Feast Day of Julian the Hospitaler,
a pious fiction who became a patron of innkeepers and travelers. Imaginary or not, Julian -- for whom at least seven churches were named -- was the subject of a strange and checkered legend in which he accidentally killed his own parents. He purportedly earned his forgiveness by opening a house for wayward pilgrims back when the word travel was more closely related to the French travail, suffering. Fyne Moryson's Itinerary (1617) offered some precautions for travelers who wished to take undue travail out of their travels: "In all inns let the traveller bolt or lock the door of his chamber; let him take heed of his chamber fellows, and always have his purse under his pillow, but always folded with his garters, or some other thing he first useth in the morning, lest he forget to put it up before he go out of his chamber."
"Fyne Moryson" is just a cool name.