Green’s Dictionary of Slang

(US campus) totally, completely; often as have something down chill, to understand or know something thoroughly.

1900		E.H. Babbitt ‘College Words and Phrases’ in DN II:i 26: chill, adj. In phrase ‘have anything down chill,’ To have perfect mastery of anything.
1900		DN II 26: Chill. In phrase ‘have anything down chill.’ To have perfect mastery of anything.
1915		DN IV 232: Have down chill, to know thoroughly.