Green’s Dictionary of Slang

a cheat, a ‘crib’.

1853		‘Cuthbert Bede’ Adventures of Mr Verdant Green (1982) I 72: Those who can’t afford a coach get a cab, — alias a crib, — alias a translation.
1876		Academy 4 Nov. 448, col. 2: The use of translations, ‘cribs,’ or ‘cabs’ as boys call them, must at some time or other engage the serious attention of schoolmasters [F&H].
1914		E. Wittmann ‘Clipped Words’ in DN IV:ii 119: cab, from cabbage. A translation clandestinely used by a student in getting up a lesson; a crib.