cant find this meaning

ἤδη τοίνυν καὶ σὺ κοινώνῃ τοῦ λόγου οὗπερ ἄρτι… 434b
This κοινώνῃ is used in the middle voice, but the lexicons do not give any middle meaning. The German edition has here κοινώνει which is the imperative, and this makes sense.