tending to cause sliding, esp because icy, greasy, wet, or polished
slippery roads
tending to slip from the grasp
said of a person: not to be trusted; shifty
said of a situation: not firmly fixed; unstable
slippery slope
a course of action that is bound to lead to trouble
slipperiness noun
[alteration of Middle English slipper, from Old English slipor]