第三者

dìsānzhě
  1. sb who is romantically involved with sb already in a committed relationship
  2. the other woman
  3. the other man
  4. third person
  5. third party (in dispute)
  6. disinterested party
  7. number three in a list

CEDICT

  1. (specifically) the other man; the other woman
  2. the other man; the other woman
  3. third party

Wiktionary

  1. 当事双方以外的人或团体。如甲乙两方订定契约，而须负连代保证责任的丙方，即为第三者。
  2. 夫妻外遇的对象或情侣移情的对象。

重編國語辭典

  1. 插足他人婚姻或恋情的人
  2. 当事双方以外的人或团体

維基詞典

Entry Composition

1 第三 dì-sān
  1. third
  2. thirdly
2 者 zhě
  1. (after a verb or adjective) one who (is) ...
  2. (after a noun) person involved in ...
  3. -er
  4. -ist
  5. (used after a number or 后 hòu or 前 qián to refer to sth mentioned previously)
  6. (used after a term, to mark a pause before defining the term)
  7. (old) (used at the end of a command)
  8. (old) this

Related entries

小三 xiǎosān
  1. mistress
  2. the other woman (coll.)
  3. grade 3 in elementary school
我比你小三歲。

I'm three years younger than you.

Source: Tatoeba

第三人称 dìsānrénchēng third person (grammar)
第三方 dìsānfāng third party
第二个人 dìèrgerén
  1. the second person
  2. (fig.) someone else
  3. third party