萬尸 (*KWOl)
In Old Korean orthography, native nouns and verbs 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 萬尸, the first character shows that this is the native Old Korean word for "ten thousand", and the subsequent character shows that the coda consonant of this word is *-l.
No native Korean word for "ten thousand" is attested in any source before 1915. However, the Sinjajeon (신자전 / 新字典), a 1915 Korean–Chinese dictionary using a wide range of previous Korean dictionaries (many of them obscure or now lost), gives the otherwise unattested word 골 (Yale: kwol) as a gloss for 萬 / 万 (wàn) "ten thousand". Some scholars have also reconstructed *kwol as a native numeral for some large number based on some rare compound words involving the syllable, most notably 골백 (golbaek, “bazillion”).
As 골 (kwol) is both a semantic and phonetic match, the Old Korean word is conventionally tentatively reconstructed as *KWOl.