Rotten Rot"ten, a. [Icel. rotinn; akin to Sw. rutten, Dan. radden. See Rot.] Having rotted; putrid; decayed; as, a rotten apple; rotten meat. Hence: (a) Offensive to the smell; fetid; disgusting. You common cry of curs! whose breath I hate As reek of the rotten fens. --Shak. (b) Not firm or trusty; unsound; defective; treacherous; unsafe; as, a rotten plank, bone, stone. ``The deepness of the rotten way.'' --Knolles. Rotten borough. See under Borough. Rotten stone (Min.), a soft stone, called also Tripoli (from the country from which it was formerly brought), used in all sorts of finer grinding and polishing in the arts, and for cleaning metallic substances. The name is also given to other friable siliceous stones applied to like uses. Syn: Putrefied; decayed; carious; defective; unsound; corrupt; deceitful; treacherous. -- Rot"ten*ly, adv. -- Rot"ten*ness, n.