Green’s Dictionary of Slang

cabbage n.4

[? cabbage n.1 (1), tailors’ scraps, thus ‘padding’; ? OF cabuse, imposture, trick; cabuser, to deceive, to cheat; also OF cabas, cheating, theft; Fr. cabasser, to pack up, to cheat, to steal; cabasseur, deceiver, thief; ‘but evidence is wanting’ (OED)]

1. deceitful talk.

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[UK]‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 81: Flummery deceptious talk. See Cabbage.

2. a ‘crib’ or other form of cheat used by schoolchildren.

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[UK]Brewer Dict. of Phrase and Fable 129: Cabbage is also a common schoolboy term for a literary crib, or other petty theft .