onychius
Could not find onychi in Logeion dictionaries.
onychi masculine genitive singular, neuter genitive singular of onychius
ŏnychĭus, a, um, adj. [onyx],
- of or belonging to onyx: onychius lapis, i. e. onyx, Tert. adv. Marc. 2, 10.
onichius lapis