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A fish breathes by swallowing water and passing it through gill slits on each side of its head. Blood-filled filaments on the gills extract oxygen from the water as it flows through.

gill 1

1. Zoology The respiratory organ of most aquatic animals that obtain oxygen from water, consisting of a filamentous structure of vascular membranes across which dissolved gases are exchanged.
a. often gills The wattle of a bird.
b. gills Informal The area around the chin and neck.
3. Botany One of the thin, platelike structures on the underside of the cap of a mushroom or similar fungus.
v. gilled, gill·ing, gills
1. To catch (fish) in a gill net.
2. To gut or clean (fish).
To become entangled in a gill net. Used of fish.
to the gills Informal
As full as possible; completely.

[Middle English gile, of Scandinavian origin.]

gilled adj.

gill 2

n. Abbr. gi or gi.
1. A unit of volume or capacity in the US Customary System, used in liquid measure, equal to 1/4 of a pint or four ounces (118 milliliters).
2. A unit of volume or capacity, used in dry and liquid measure, equal to 1/4 of a British Imperial pint (142 milliliters).

[Middle English gille, from Old French, wine measure, from Late Latin gillō, vessel for cooling liquids.]

gill 3

n. Chiefly British
1. A ravine.
2. A narrow stream.

[Middle English gille, from Old Norse gil.]

gill 4

also jill or Gill  (jĭl)
n. Obsolete
A girl, often one's sweetheart.

[Middle English gille, from Gille, a woman's name.]


pl n
1. (Zoology) (sometimes singular) the wattle of birds such as domestic fowl
2. green around the gills green about the gills informal looking or feeling nauseated
References in classic literature ?
Anomalous as it may seem, this is precisely the case with the whale, who systematically lives, by intervals, his full hour and more (when at the bottom) without drawing a single breath, or so much as in any way inhaling a particle of air; for, remember, he has no gills.
They eat it raw; scales, bones, gills, and all the inside.
Madam," I said, breathlessly springing forward, as a heavenly being was coldly tearing the hook from the gills of the unlucky trout, "though I am a stranger, will you do me a great favour?
There the nets brought up beautiful specimens of fish: some with azure fins and tails like gold, the flesh of which is unrivalled; some nearly destitute of scales, but of exquisite flavour; others, with bony jaws, and yellow-tinged gills, as good as bonitos; all fish that would be of use to us.
The birds then collected at a short distance, yet to near that their naked necks, entirely bare of feathers, could be plainly seen, as they stretched them out with the effort of their cries, while their gristly crests, garnished with a comb and gills of deep violet, stood erect with rage.
Nope, it ain't the valley of the moon," agreed Billy, and he said it on the evening of the day he hooked a monster steelhead, standing to his neck in the ice-cold water of the Rogue and fighting for forty minutes, with screaming reel, ere he drew his finny prize to the bank and with the scalp-yell of a Comanche jumped and clutched it by the gills.
The salmon, swimming near the surface, as is their custom, run their heads through these meshes, and are prevented from going on through by their larger girth of body, and from going back because of their gills, which catch in the mesh.
My heart fell down amongst my lungs and livers and things, and a hard piece of corn-crust started down my throat after it and got met on the road with a cough, and was shot across the table, and took one of the children in the eye and curled him up like a fishing-worm, and let a cry out of him the size of a warwhoop, and Tom he turned kinder blue around the gills, and it all amounted to a considerable state of things for about a quarter of a minute or as much as that, and I would a sold out for half price if there was a bidder.
I have fished for trout, in Tahoe, and at a measured depth of eighty-four feet I have seen them put their noses to the bait and I could see their gills open and shut.
A healthy young slip of a gale from the breath iv it, sir," he answered, "with a splatter iv rain just to wet our gills an' no more.
But so long goes the pot to the water, men say, at last comes it home broken," cries Gill.
Gill told me, he had been employed professionally to examine one: he found the passage low, narrow, crooked, and not of uniform breadth, but of very considerable length.