imperjūrātus (inp-; -pējūr-), a, um, adj. [2. in-periuratus],
that is never sworn falsely by , a poet. epithet of the Styx: aquae, Ov. Ib. 78.
imperiūrātus (in-p-) adj., by which no false oath is taken: aquae (of the Styx), O. ...
An Elementary Latin Dictionary