一理ある (いちり ある, ichiri aru) means “(someone’s argument) is true in a way”. It is often used when you show some recognition of someone’s statement while providing an opinion to counter it, as in “それは一理あるが、しかし…” meaning “That is true in a way, but …”. You can also use this word when you more or less agree with someone.
Nowadays, young people use 一理ある in a casual way on the Internet when they agree with someone. In this case, it rather means “That’s true”, “You’re right” or “agreed”.
一理ある consists of two parts “一理” and “ある”. The former literally means “one rationale”, and the latter means “(a thing) exists”. Therefore, 一理ある indicates that there exists at least one rationale or truth behind someone’s statement.
Some people say “Today there is no need to go to university because we can study by ourselves whatever we want to on the Internet.” This statement is true in a way, but we should not forget that the university offers precious opportunities for us to meet our lifelong friends.
Although his remarks are provocative, they are true in some respects.
A: Why did you quit Twitter?
B: Cause it’s a waste of time.
A: That’s true.
Synonyms: 確かに (That’s true; You’ve got a point)
Synonyms in English: true in a way, true in some respects
Related words and phrases: 一 (one), 理(rationale, reason), ある (exist)