"organ of breathing in fishes," early 14c., of unknown origin, perhaps related to Scandinavian words, such as Old Norse gjölnar which perhaps means "gills," and Old Danish -gæln (in fiske-gæln "fish gill"); said to be ultimately from a PIE *ghel-una- "jaw" (cognate: Greek kheilos "lip"). Related: Gills.

liquid measure (commonly a half-pint), late 13c., from Old French gille, a wine measure, and from Medieval Latin gillo "earthenware jar," words of uncertain origin, perhaps related to the source of gallon.