What is the X in X-mas?
early 14c., "headband," from Old French filet (12c.) "thread, filament; strip, ligament," diminutive of fil "thread" (see file (v.)). Sense of "cut of meat or fish" is from late 14c., apparently so called because it was prepared by being tied up with a string. As a verb, from c.1600, "to bind with a narrow band;" meaning "to cut in fillets" is from 1846. Related: Filleted; filleting.
fillet fil·let (fĭl'ĭt)
A loop of cord or tape used for making traction on a part of the fetus.
A loop-shaped band of fibers, especially the lemniscus.
(from Latin filum, "thread"), in architecture, the characteristically rectangular or square ribbonlike bands that separate moldings and ornaments. Fillets are common in classical architecture (in which they also may be found between the flutings of columns) and in Gothic architecture. In the Early English and Decorated styles of the 13th and 14th centuries, respectively, the fillet is frequently worked upon larger moldings and column shafts; in these cases it is not always flat but rather is sometimes cut into two or more narrow faces that have sharp edges between them. See also molding