sitz bath
Concise Oxford English Dictionary © 2008 Oxford University Press:
sitz bath /ˈsɪts/
▶noun a bath in which only the buttocks and hips are immersed in water.
– origin C19: partial translation of Ger. Sitzbad, from sitzen ‘sit’ + Bad ‘bath’.
'sitz bath' also found in these Oxford entries:

