一回事

yīhuíshì
  1. one and the same (thing)
  2. one thing (as distinct from another)

CEDICT

Entry Composition

1 一 yī
  1. one
  2. single
  3. a (article)
  4. as soon as
  5. entire; whole; all; throughout
  6. "one" radical in Chinese characters (Kangxi radical 1)
  7. also pr. yāo for greater clarity when spelling out numbers digit by digit
2 回事 huíshì (old) to report to one's master