/oh"veuhr koyl'/ , n. Horol.
1. a fixed end of a spiral hairspring, consisting of an upwardly and inwardly bent continuation of the outermost coil of the spring: used to offset the asymmetry of the common spiral spring when tight, which impairs isochronism.
2. a hairspring having such a fixed end.
[ 1880-85; OVER- + COIL 1 ]