I was just watching While You Were Sleeping and she says: 석 달전 쯤에 꾼 꿈인데..
I'm confused about what 석 is and when it's used as the number three. Are there equivalents for other numbers as well?
Korean Language Stack Exchange is a question and answer site for linguists, teachers and students of the Korean language. It only takes a minute to sign up.
Sign up to join this community석 is one of the old quantifiers conventionally used by the elder people in Korea. There are many old quantifiers in Korean. For example, other than 세, there is also 서 which has the meaning of three. Some old Korean proverb:
구슬이 서 말이라도 꿰어야 보배
→ (literally) It takes more than three 말 (18 liters) of pearls to make a necklace.
→ Nothing is complete unless you put it in final shape.
The Rules of Standard Korean Language (표준어 규정) say that nouns ~돈, ~말, ~발, ~푼 must be used with 서 (such as 서 말 and 서 푼) and ~냥, ~되, ~섬, ~자 has to be used with 석 (such as 석 냥, 석 되). However these nouns are quite old words, and one might encounter them in some Korean historical movies or dramas.
Other old quantifiers include 너 (four), 닷 (five), 엿 (six) etc.
Nowadays, 세 is used more often and actually is a recommended form of the The National Institute of Korean Language (국립국어원).
'세', '석'이 단위 명사와 자연스럽게 어울려 쓰인다면, 둘 다 표준어로 인정하되, '세'를 원칙 표기로 보고 있습니다.
If both '세' and '석' is used naturally with nouns having a meaning of unit, both are standard Korean, but '세' is recommended.
So both 석 달 and 세 달 are standard Korean, but Koreans use 세 달 more often.
세 달 (석 달) and 삼 개월 are almost identical in meaning, just that words originated from Hanja (삼 개월: 三個月) have more formal nuance. In addition, maybe 석 달 has a feeling of a person above 40s is speaking (just my opinion).
셋 달 is awkward since both 셋 and 달 are nouns. In Korean, when saying about some quantity, we have to use words of 관형사 (similar to adjectives in English). For example,
세 사람, 네 그릇, 두 컵
Three people, four plates, two cups
하나, 둘, 셋, 넷 are used as nouns in sentences:
셋은 앞으로도 늘 함께 지내기로 맹세했다.
The three pledged to be always together from now on.