Words that are very similar sounding in Teochew

One of the reason why I wanted to start to learn Hangugeo is due to the fact that many words that I stumbled upon were about 95-99% the same as in Teochew language, the "ancient" language my grandmother used. This language is just spoken by about 15-20 million people.

Here are some words that are similar:
1) 학생 (hak saeng) - student
2) 책 (chaek) - book
3) 기회 (ki hw-oe) - chance
4) 진심 (jin sim) - wholeheartedly
5) 남섹 (nam saek) - dark blue colour

These words are pronounced exactly the same.

What is the connection that some words are exactly the same?

According to one research, the roots were from the even ancient language of 5000-7000 years ago. And the "tribes" of Korean and Teochew still used these ancient words, hand down from generations. 

While other words were replaced. Modified. But things like "student" is as old as time. So it remains. Will add more as I discover more similar words.