A. 그러니 B. (B is often a suggestion or command) · more common in speech: 그러니까
so, therefore (so you should …)
Example
내일 비가 온대요. 그러니 우산 꼭 챙기세요.
They say it'll rain tomorrow. So be sure to take an umbrella.
Word parts
그렇다 'to be so' + -(으)니 'since': 'since it is so'.
Good to know
A shorter, slightly more written form of 그러니까. Like 그러니까 — and unlike 그래서 — it can be followed by commands and suggestions.