重中之重

zhòngzhōngzhīzhòng
  1. of the utmost importance
  2. of highest priority

CEDICT

Entry Composition

1 重 zhòng
  1. heavy
  2. serious
  3. to attach importance to
2 中 zhōng
  1. within; among; in
  2. middle; center
  3. while (doing sth); during
  4. (dialect) OK; all right
3 之 zhī
  1. (possessive particle, literary equivalent of 的 de)
  2. him
  3. her
  4. it
4 重 zhòng
  1. heavy
  2. serious
  3. to attach importance to