Green’s Dictionary of Slang

gills n.1

[SE gill, a fish’s breathing apparatus, situated on each side of the neck]

1. [17C+] the cheeks; often in phr. red in the gills or pink in the gills, embarrassed.

2. [19C] the corners of a stand-up shirt-collar.

3. [mid–late 19C] the mouth.

In phrases

down in the gills

[mid-19C+] depressed.

for one’s gills (adv.)

[mid-19C] (UK Und.) to one’s gain, to one’s advantage.

grease one’s gills (v.) (also grease the gills)

[late 19C–1900s] to eat heartily and substantially.

green about the gills (adj.) (also green around/in/round the gills, blue..., greenish...)

[late 19C+] feeling and looking sick, esp. from an excess of alcohol.

pink around the gills (adj.)

[1960s] (US campus) drunk.

red about the gills (adj.) (also red in the gills)

[mid-19C–1900s] angry, choleric.

to the gills (adv.)

[mid-19C+] absolutely, completely.

white about/around/in/round the gills (adj.)

1. [mid-19C+] frightened.

2. [mid-19C+] (also pale about/around/round the gills) feeling and looking sick, esp. from an excess of alcohol.