子丑寅卯 [－－－－]

Jyutping zi2 cau2 jan4 maau5
Pinyin zǐ chǒu yín mǎo

Definitions (Wiktionary)
  1. phrase, figuratively, idiomatic
    underlying reasons or logic; main threads (of a complicated affair)
  2. phrase, idiomatic, literally
    zi, chou, yin and mao (the first four earthly branches)