Many Japanese words have roots in Korean, just like many Korean words have roots in Chinese. While each language(s) is unique and very distinctive from each other, influence from neighboring nations is very common. Many times words may only be vaguely similar as they evolved and changed from local accents and use. As China was the great superpower in the region for many centuries knowledge tended to radiate geographically outward from there. If you want to see current examples, think of Korean and Japanese words that have been merged with American English (due to presence not geography in this case.) Some of them sound similar to the English version, others sound only vaguely like it. This is only skimming the surface of a very deep pool.