Korean Grammar Dictionary

-려거든 【벼락을 치실려거든 [ edit | delete | edit examples ]
연결어미 Connective ending (연결어미 Connective ending)
『 』
From -(으)려(고) (하)거든 (i.e., intentive -려 + provisional -거든): provided that, if/when (usually followed by command, suggestion, or promise).

벼락을 치실려거든 (빙하기 )
if you intend to strike with thunder ...