-으이-

• -이- (-i-) — after vowels and ㄹ (l)

From Middle Korean -으〮ᅌᅵ/ᄋᆞ〮ᅌᅵ- (Yale: -úngì/óngì-, addressee-honoring suffix).

-으이- • (-eu'i-)

1. (archaic or Gyeongsang) A suffix adding an intensified degree of politeness or deference.

   아부지, 떡 좀 잡수이소. (Gyeongsang dialect, Changwon)

   Abuji, tteok jom japsu-i-so.

   Father, have some rice cakes.

   孟(맹)子(자)ㅣ 對(대)曰(왈) 於(어)傳(전)에 有(유)之(지)하니이다. (traditional cantillation of Mencius)

   Maengja(e) daewal eojeon-e yuji-ha-ni-i-da.

   Mencius replied, "It is so in the records."

(archaic):

• Common in Middle and Early Modern Korean, in the standard language, it is nowadays largely restricted to the archaic language of religious texts, such as the Bible, Buddhist prayers, or cantillation of the Confucian canon.

(Gyeongsang):

• In contemporary Gyeongsang, it attaches only to -소 (-so) and -읍시다 (-eupsida), the imperative and hortative suffixes of the semi-formal style respectively, to form -으이소 (-eu'iso) and -으입시다 (-eu'ipsida), the imperative and hortative moods of the formal polite style respectively.
• The formal polite style is less formal in Gyeongsang than in contemporary Seoul Korean, and hence can be used by e.g. a child addressing one's parents. In these contexts, it coexists with the polite style formed by -예 (-ye).
• This suffix is not used in northwestern Gyeongsang (e.g. Andong).