"organ of breathing in fishes," early 14c., of unknown origin, perhaps from a Scandinavian source, e.g. Old Norse giolnar which perhaps means "gills;" Old Danish -gæln (in fiske-gæln "fish gill"). Related: Gills.
liquid measure (commonly a half-pint), late 13c., from Old French gille, a wine measure, and directly from Medieval Latin gillo "earthenware jar," of uncertain origin.
Sick-looking; pale and miserable; nauseated: He was looking green around the gills, so I told him to lie down
[1930s+; the date should probably be earlier; gills, ''face,'' is found by 1626]
Looking sickly or nauseous (1959+)