後是 (*TWUy, *TWUri)
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 後是, the first character shows that this is the native Old Korean word for “back; afterwards”, and the subsequent character(s) show(s) that the coda consonant of this word is *-y. Because the semantics and the final phoneme(s) match, the word is conventionally reconstructed as *TWUy, the ancestor of Middle Korean 뒿〯 (Yale: twǔyh). Note that the reconstruction was not necessarily the actual pronunciation. Rather, it should simply be considered as a method of representing an Old Korean form phonetically by using its Middle Korean reflex.
According to scholarly convention, the elements of the reconstruction which are not directly represented by phonograms are given in capital letters. This allows readers to identify what part of the reconstruction is attested and what part is applied retroactively from the Middle Korean reflex.
Although obscured by the logographic nature of the orthography, the Old Korean stem for "back; afterwards" (or at least its earlier form) is believed to have been disyllabic. The Middle Korean reflex 뒿〯 (Yale: twǔyh) has a bimoraic rising tone, which is the result of a merger of a low-pitch and high-pitch syllable. In particular, rising-tone stems ending in the glide *-y are often the result of an intervocallic consonant being elided before */-i/.
One of the placename glosses in the Samguk sagi has an element phonographically spelled 助利 (MC dzrjoH lijH), with the apparent meaning of "north". If this is to be connected to 뒿〯 (Yale: twǔyh), one of whose meanings is "north", the lost consonant may have been */-r-/.
The Middle Korean reflex has a final /-h/ which may be the remnant of an ancient place-related suffix */-k/ (see Appendix:Middle Korean h-final nouns). This is either absent in the interpretative gugyeol corpus, or possibly incorporated with the locative ending *-uy, as the word mainly occurs in the locative case as 後是中 (*TWUyk-uy).