非同小可

fēitóngxiǎokě
  1. extremely important
  2. no small matter

CEDICT

no small (or trivial) matter

Wiktionary

  1. 形容事情的重要或情况严重。
  2. 形容人的学问或本领不同寻常。《儒林外史．第四七回》：「话说虞华轩也是一个非同小可之人。」《文明小史．第二九回》：「这位大绅乡非同小可，乃曾做过出使英国钦差大臣。」也作「非通小可」。

重編國語辭典

Entry Composition

1 非 fēi
  1. to not be; not
  2. wrong; incorrect
  3. non-; un-; in-; de-
  4. to reproach; to blame
  5. (coll.) to insist on; simply must
2 同 tóng
  1. like
  2. same
  3. similar
  4. together
  5. alike
  6. with
3 小可 xiǎokě
  1. small
  2. unimportant
  3. (polite) my humble person

Related entries

至关重要 zhìguānzhòngyào
  1. extremely important
  2. vital
  3. crucial
  4. essential
摩天大厦里的电梯是至关重要的。

The elevators in a skyscraper are vital systems.

Source: Tatoeba

切要 qièyào
  1. essential
  2. extremely important