What's the honorific to represent a female's older sister?

Question

I got to know that Korean grammar uses an extensive system of honorifics and those are used to differentiate between formal and informal speech.

So ways to formal speech is to honorific nouns and verbs.I was searching for these and found a wiki page which give some examples on how to use but I'm unable to find out :

• How to formally call 언니 (female's older sister) ? Can we use eonnim or (eonninim) ?
• Why the honorific for 오빠 (oppa) became 오라버니 (orabeoni) instead of oppani or oppanim ?

For the first one it has already ni suffix in eonni and that's why I guess there is no honorific, if this is the case how do call eonni informally or as a person who is on the same level/same social status.

Answer 1

"오라버니" has a long history in its etymology and actually it comes from Chinese characters, 오(吾)-압(亞)-아(御)-이(爾).

압(亞)-아(御)-이(爾) (it became 아버지, 어버이) means a 'father' and 오(吾) means a 'brother'. It literally translates to "brother father". In old days in Korea, when a father died, the eldest brother acted as a father of a family.

It has nothing to do with '오빠' etymologically, but became an honorific noun for it. You can never use '오빠니' as it doesn't make any sense. '오빠님' could be used for a joke, but nobody uses it to mean '오라버니'.

There is no honorific noun for '언니' because there was no counterpart of 오(吾)-압(亞)-아(御)-이(爾) in the past. You should not use "언니님" unless you are making a joke.

Answer 2

There seems to be no honorific expression of 언니.

{언니}는 여성끼리의 호칭어다. 앞서 확인한 다른 호칭어와 같이 친족 집단에서 사용되며 비 친족 집단에서 [친밀]의 공유를 중심으로 사용되는 공통점을 가진다. 하지만 다른 어휘소가 {형님}, {오라버니}, {누님}같은 확장 어휘소를 가지는 것과 달리 {언니}는 별도의 확장 어휘소가 없으며 [높임]을 표현할 때는 (3 "6")처럼 {형님}을 사용한다.¹

Here (3 "6") is the sixth meaning of "형님".

Reference

1. 김광순 (2015). 친족어의 호칭어로서 확장ㆍ사용 양상. 한국어의미학, 48, 175-201.