jack, n.¹⁵ — Green’s Dictionary of Slang

jack n.¹⁵

[? play on SE jackass, i.e. the sort of student who requires a crib; or ? SE jack, i.e. it ‘lifts up’ grades]

(US campus) a translation or hidden notes.

1900		E.H. Babbitt ‘College Words and Phrases’ in DN II:i 43: jack, n. 1. A translation. 2. Concealed notes for use in examination or recitation.
1906		J.W. Carr ‘Words from Northwest Arkansas’ in DN III:ii 142: jack, n. [...] 2. A literal translation. ‘He always gets his latin with a jack’.