According to Babiniotis it is a μικρή, συνήθως, υπόγεια ταβέρνα όπου προσφέρεται κυρίως βαρελίσιο κρασί συχνά με φαγητό σε χαμηλές τιμές.
From the Turkish kütük meaning a log or tree stump, and the expression kütük gıbı (= blind drunk).
I think Babiniotis is wrong in using “υπόγεια” as they are not underground; “ημιυπόγεια” (semi-basement) might be a better description as, traditionally, though the κουτούκι floor was below street level, the windows were level with the street. Diners could see passers-by from the knee downwards.
There’s more in this article. I doubt the final three make the count in strict κουτούκι terms, but some of them are definitely worth a visit. One of my projects for 2026.
https://www.ekathimerini.com/leisure/gastronomy/1288905/what-%CE%B9s-a-koutouki
Finally, Katouni Street gets more than one mention, which makes me miss the Dubliner even more.