Cf. Photius beta16; Adler also cites Lexicon Ambrosianum 234.
[1] In Greek, the difference is between the active imperative and, here, the middle imperative. This is one of only a very few attestations of a middle form of this verb, apart from future tense forms, and the only one from prior to the common era.
[2] Cratinus fr.391 Kock (421 Kassel-Austin). Kock suggests this word was spoken by a character being lampooned for soloecisms (in this case, using a middle form where an active form is appropriate), like Datis in Aristophanes Peace 289 ff. (Web address 1).