子丑寅卯

zǐchǒuyínmǎo
  1. (figurative) underlying reasons or logic; main threads (of a complicated affair)
  2. (literally) zi, chou, yin and mao (the first four earthly branches)
  3. underlying reasons or logic; main threads (of a complicated affair)
  4. zi, chou, yin and mao (the first four earthly branches)

Wiktionary

Entry Composition

1 子丑 zǐchǒu
  1. first two of the twelve earthly branches 十二地支
  2. by ext., the earthly branches
2 寅 yín
  1. 3rd earthly branch: 3-5 a.m., 1st solar month (4th February-5th March), year of the Tiger
  2. ancient Chinese compass point: 60°
=3 卯 mǎo
  1. mortise (slot cut into wood to receive a tenon)
  2. 4th earthly branch: 5–7 a.m., 2nd solar month (6th March–4th April), Year of the Rabbit
  3. ancient Chinese compass point: 90° (east)
  4. (coll.) to concentrate one's strength (variant of 铆 mǎo)
=3 卯 mǎo variant of 卯 mǎo
=3 卯 mǎo old variant of 卯 mǎo