一丝一毫

一絲一毫
yīsīyīháo
  1. one thread, one hair (idiom); a tiny bit
  2. an iota

CEDICT

a tiny bit; an iota; a trace

Wiktionary

形容极其细微。

重編國語辭典

形容极其细微

維基詞典

Entry Composition

1 一丝 yīsī a tiny bit
2 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
3 毫 háo
  1. hair
  2. drawing brush
  3. (in the) least
  4. one thousandth
  5. currency unit, 0.1 yuan