Source : Webster's Revised Unabridged Dictionary (1913)

Oillet \Oil"let\, n. [See {Eyelet}.] (Arch.)
   (a) A small opening or loophole, sometimes circular, used in
       medi[ae]val fortifications.
   (b) A small circular opening, and ring of moldings
       surrounding it, used in window tracery in Gothic
       architecture. [Written also {oylet}.]