hemihydrate
noun
hemi·hy·drate ˌhe-mi-ˈhī-ˌdrāt 
: a hydrate (such as plaster of paris) containing half a mole of water to one mole of the compound forming the hydrate
hemihydrated
ˌhe-mi-ˈhī-ˌdrā-təd
adjective 
Word History
First Known Use
circa 1901, in the meaning defined above