Green’s Dictionary of Slang

down n.2

1. [early–mid-19C] (UK Und.) a suspicion, a degree of illegality; thus take down off, to render a (stolen) object less suspicious; there is no down, there is no risk.

2. [mid-19C+] (orig. Aus.) a prejudice against, a suspicion of; a tendency to be unkind towards; usu. as have a down on.

In derivatives

downment (n.)

[mid-19C] (UK und.) sharp practice, deception.

In phrases

put a down (up)on (v.)

[19C] to inform against someone.

raise the down (v.)

[early 19C] (Scot. Und.) to give the alarm.