spell, n.² — Green’s Dictionary of Slang

spell n.²

[SE spell, a short time]

1. (UK Und.) a two-year sentence.

1835

Worcester Herald 26 Dec. 4/3: Spell, two years.

2. a sentence of three months’ imprisonment.

1885		Bulletin (Sydney) 21 Mar. 22/3: We are bursting the bars of our prison, / We are now from the spell half-released, / And the light of a sun newly risen, / Is shedding a glow in the East.
1918		D.G. Rowse Doughboy Dope 9: Czyerznski only ducked a spell in the jug by handshaking with the top-kick due to going AWOL.

spell job (n.)

(Ulster) a job of uncertain or indefinite duration.

1983

J. Pepper Illus. Encyc. Ulster Knowledge n.p.: ‘If only I’d known it was a spell job,’ he said, ‘I’d nivver have taken it.’ [BS].