You can remember the meaning of 回合 with this easy mnemonic:
After a knee injury, the past boxing champion has <strong>returned</strong> (回) to the ring to meet his rival once again a first <strong>round</strong> of the day. This time with a vengeance for the wilful injury the other inflicted on him. The champ wishes to <strong>close</strong> (合) the past and start a new chapter in his career.
Using mnemonics to remember the meaning of Chinese characters like can have an enormous impact on how long to learn Mandarin it takes.