Source : Webster's Revised Unabridged Dictionary (1913)

Sitz bath \Sitz" bath`\ [G. sitzbad.]
   A tub in which one bathes in a sitting posture; also, a bath
   so taken; a hip bath.

Source : WordNet®

sitz bath
     n : a bathtub in which your buttocks and hips are immersed as if
         you were sitting in a chair and you bathe in a sitting
         position [syn: {hip bath}]