Definition of "gill"

Fishes […] perform their respiration under water by the gills.

1691, John Ray, The Wisdom of God Manifested in the Works of the Creation. […], London: […] Samuel Smith, […]

dropsy fills you to the gills

1728, Jonathan Swift, Ballad on Ballyspellin

As we had fish home in the icebox, when Bill led the fish up alongside, I leaned over the combing, gilled the fish with my fingers, slid out the hook and let go. The bass lay there for a moment, tired from the arch of the rod and the pull of the line.

1948, Oliver Hazard Perry Rodman, The Saltwater Fisherman's Favorite Four, page 166

She gutted and gilled the fish, then scaled it.

2014, Scott Tippett, Polaris, page 99

Owing to the peculiar shape of the pompano and the relatively large mesh in the pompano gill nets, the fish are not caught by being actually gilled.

1898, Report of the Commissioner of Fisheries to the Secretary of Commerce and Labor, page 255

In cases of very heavy catches the nets may be hauled and stored with the fish still gilled. The fish would then be shaken out on return to the port.

1971, Michael Culley, G. A. Kerkut, The Pilchard: Biology and Exploitation page 70

The intention is to gill the fish, so they are usually scared into the net by rowing one boat into the middle of the net circle and banging the oars on the boat bottom or splashing the water.

1994, G.D. Pickett, M.G. Pawson, Sea Bass: Biology, page 177

Since the fine threads of the net usually are caught under the gill covers of the fish they are said to be "gilled."

1926, Walter Koelz, Fishing industry of the Great Lakes, page 556

Also, when fish gilled there wasn't as much extra twine to tangle in, so they were easier to release from the net.

2010, Edward A. Perrine, Midnight Tracy, page 147

Gill comes from the Knight, that did so seek / To gaine her love; she's hir'd for a week.

1646, Humphrey Mill, “Section XXI”, in The Nights Search, Part 2‎, page 129

Comme proprement le fine of my Designs dey make; / Dam gilling Whore / Et Louis d'or

1719, Henry Playford, “Lewis Upon the Fret”, in Wit and Mirth: Or, Pills to Purge Melancholy, page 72