From the root *PWUSkul- + the verb-forming suffix 是 (*-i).
慚肸伊 (*PWUSKuli- or *PWUSKuri-)
This word is attested from the hyangga poem Heonhwa-ga.
In Old Korean orthography, native terms with clear Chinese equivalents are usually written with an initial Chinese character (logogram) glossing the meaning of the word, followed by one or more Chinese characters (phonograms) that transcribe the final syllable or coda consonant of the term. In the case of 慚肸伊, the first character shows that this is the native Old Korean word for "to be ashamed", while the subsequent characters show that the final two syllables were *-u(l/r)i. Because the semantics and the final phoneme(s) match, the word is conventionally reconstructed as *PWUSKu(l/r)i-, the ancestor of Middle Korean 붓그〮리〮다〮 (Yale: pwùskúlí-tá, “to be ashamed”)
Middle Korean merged Old Korean *r and *l unconditionally, and it is not always easy to determine the Old Korean phoneme based on the Middle Korean reflex. Old Korean reconstructions are conventionally given in the Yale Romanization of Korean, which makes only those phonemic distinctions also made in Middle Korean. However, Alexander Vovin gives circumstantial evidence that the phonograms in this word represent *-ul-i, with a lateral consonant. Note that 肸 or 肹 is usually reconstructed as *-(h)ur with a rhotic, requiring a reading of *-ul-i to slightly modify its value.