Comments:SKE 113-114, EAS 102. The Kor.-Jpn. forms are not quite regular: in Kor. one would rather expect *kɨ́sìrk (so probably we are dealing with a metathesis); the diphthong -ui- in Japanese (as in the few other similar cases) has a not quite clear origin. It may well be that the Jpn. form is related to *kui 'fortress' < *'border', see *ki̯udu - although the suffixation is peculiar.
