Ill with, as in He's down with the flu. The down here alludes to being felled by illness. Also see come down with.
Depose, do away with, as in Down with the king! This imperative dates from the early 1500s.
Lower or put something down, as in Down with the mainsail. [Mid-1600s]
be or get down with. Be close friends with, as in I'm down with that crowd. [Slang; late 1900s]