- number one; the first or primary
- (by extension) most; -est
- (forms superlatives of adjectives)
- 그 사전은 제일 좋아요.
- Geu sajeon-eun jeil joayo.
- This dictionary is the best.
The most common use of this is in front of an adjective or adjectival phrase, to denote superlativity.
A 2007 decision by the Patent Court of Korea found that while the superlative sense of 제일 is not distinctive, the use of 제일 in front of a noun is distinctive and can be protected by trademark.