The Collaborative International Dictionary
Semicupium
Semicubium \Sem`i*cu"bi*um\, Semicupium \Sem`i*cu"pi*um\, n. A half bath, or one that covers only the lewer extremities and the hips; a sitz-bath; a half bath, or hip bath.
Wiktionary
semicupium
n. (context archaic English) A half bath, or one that covers only the lower extremities and the hips; a sitz bath.