The headword is the present participle, masculine nominative singular, of the verb katoi/omai. It has the same or similar glossing in other lexica, including Hesychius, and (as Adler notes) H's entry suggests a connection with the occurrence of katoinwme/nos (sic: "drunken") in Habakkuk 2:5 LXX.
[1] As C. Theodoridis points out in his Photius edition (vol.II p.LXIII), the adverb 'arrogantly' seems to be a textual emendation by the Suda lexicographer for the related adjective, u(perh/fanos, that he found in his immediate sources.