Same or similar entry elsewhere: references at Photius omicron404 Theodoridis. Latte on Hesychius omicron1030 regards the headword as drawn from the Septuagint (he cites Leviticus 11.4, accusative plural), but there are numerous other possibilities. For the headword, here nominative plural, see also omicron 464 (nominative singular).
The import of the first glossing word is not self-evident, but Theodoridis quotes Naber's comment on it (following Letronne), adducing Arrian, Anabasis 7.27.1: the story of the murder of Alexander the Great by the administration of poison kept in a mule's hoof. (We do not know whether the word was used also for the normal pyxis, the small box made of boxwood, or in some other sense of the word. It is unrelated to hoplite and hopla, omicron 466, etc.)