The Collaborative International Dictionary
Oillet \Oil"let\, n. [See Eyelet.] (Arch.)
A small opening or loophole, sometimes circular, used in medi[ae]val fortifications.
A small circular opening, and ring of moldings surrounding it, used in window tracery in Gothic architecture. [Written also oylet.]
Wiktionary
n. (context medieval architecture English) A round hole or circle with which an opening for an arrow slit terminates.
Usage examples of "oillet".
The things were full of cobwebs and dead insects and rat turds, poorly lit by the occasional inward-looking peephole or narrow slits or oillets in the exterior masonry.
Another of his mistresses, Madame des Oillets, had bought a love charm for the king, which had been concocted by a priest from menstrual blood - from the lady - and sperm from a man, who masturbated into a chalice.