κοὐ (kou)
κοὐ is an Ancient Greek form of οὐ, meaning “not”. It is the adverb.
It can also be a form of πού, “somewhere, I suppose, perhaps”.
Found 195 times in the Ancient Greek texts on Socratos.
Where it is used
Theocritus, Εἰδύλλια 6.22: κοὔ μʼ ἔλαθʼ, οὔ, τὸν ἐμὸν ἕνα τὸν γλυκύν, ὧ ποθόρημαι
Euripides, Cyclops 376: κοὐ πιστά, μύθοις εἰκότ’, οὐδ’ ἔργοις βροτῶν;
Euripides, Hecuba 463: σὺν Δηλιάσιν τε κού-
Source: Socratos (socratos.org), a free reader for Ancient Greek and Latin. Grammar from the Perseus Treebank and Morpheus; dictionary entries from Liddell-Scott-Jones, A Greek-English Lexicon (Perseus Digital Library, CC BY-SA). Counts are from the texts on Socratos.