* 되거든 = 되다 + -거든. * 되다 = 1. to work out. "말이 (안) 된다" = It (doesn't) makes sense. 2. to become (something). "의사가 되었다" = (He) became a doctor. * -거든 = 1. emphatic sentence ending: "I'm telling you it is/does so", 2. explanatory ending: "the reason is because ..." , 3. verb ending for "once (something happens"). So 되거든 can mean any of the combinations above. The meaning can also depend on the intonation. One common example is a contradicting response to someone who says something won't work. A: 그거 그렇게 하면 안 돼. = It's not going to work if you do it like that. B: 아니, 되거든! = Don't give me that. I know it will!