i really dont know how to explain the different between them clearly. So, i give u some example : -Kết thúc: often use when talk abt something almost end or over +kết thúc chương trình/phim/1 mối tình/sự nghiệp the opposite word: mở đầu -Cuối: sometime it's can use like "kết thúc" but often in daily conversation, +like cuối phim/cuối chương trình(but not really mean this program or film is really over) +the main different is often use to talk abt things: cuối đường/cuối năm/cuối tuần/cuối ngày(these things never over, just start and end and then start again) +often use with "cùng": this situation almost like kết thúc=cuối cùng thì... the opposite word: đầu idiom:cùng trời cuối đất -Hết:mean u have something and u use/lose/spend it all, like kết thúc in some case when daily conversation but in some situation not same way of use +when u wanna say u spend all ur money and it's no money: hết tiền(cant use kết thúc or cuối). And some others situation: hết thời gian, hết sức lực/mức(when u wanna say u already used ur all ability, cant try anymore), hết yêu,hết lòng( work with all u have) +when u have sickness and it's over: hết bệnh, hết mụn,hết đau lưng,.... +sentence use to express feeling , when u lost something really important,lol: hết rồi, hết thật rồi....(maybe wen u watching tv or film u can hear it) the opposite word: còn i only remember these, if u have anything u dont know u can ask me. And im sr my English not really good, hope u understand it all. lol