boot hill, n. — Green’s Dictionary of Slang

boot hill n.

[orig. Western Boot Hill, in Dodge City, the cemetery set aside for those who died ‘with their boots on’, i.e. in a gunfight]

(US)

1. a cemetery.

1921		Alliance Herald (NE) 19 Aug. 4/3: [They] carted the body off to the local boot hill and dumped it in a shallow grave.
1947		W.D. Overholser Buckaroo’s Code (1948) 31: Maxon never was anything but a hard case who drank too much [...] and now he’s ready for boothill.

2. a prison cemetery.

1935		A.J. Pollock Und. Speaks 11/2: Boot hill, prison cemetery.
1947		J.W. Arnold ‘The Language of Delinquent Boys’ in AS XXII:2 Apr. 121: Boot hill. Boy’s Industrial School Cemetery.
1960		(con. 1950-1960) R.A. Freeman Dict. Inmate Sl. (Walla Walla, WA) 16: Boot-hill – a prison cemetery.

3. (N.Z. prison) a prison.

2001

D. Looser Boobslang [U. Canterbury D.Phil. thesis] 27/2: boot hill n. prison.