천
cheon · TOPIK 1
one thousand
천 = hanja 千 (thousand), same root as Chinese qiān and Japanese sen
천 is the Sino-Korean reading of 千. Chinese qiān, Japanese sen and Korean cheon all descend from one word, so knowing any of them gives you this one. It stacks like a unit: 삼천 = three + thousand = 3,000.