其一

qíyī
  1. one of the given (options etc)
  2. the first
  3. firstly

CEDICT

Entry Composition

1 其 qí
  1. his
  2. her
  3. its
  4. their
  5. that
  6. such
  7. it (refers to sth preceding it)
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

Containing this entry

只知其一，不知其二 zhǐzhīqíyī,bùzhīqíèr to know the first, but not know the second (idiom); only partial information
二者必居其一 èrzhěbìjūqíyī
知其一不知其二 zhīqíyībùzhīqíèr

Related entries

头一 tóuyī the first
你只需要回答頭一個問題。

You have only to answer the first question.

Source: Tatoeba