詞窮

词穷
cíqióng
to not know what to say; to be lost for words

CEDICT

to be unable to give a response as one is in the wrong or has given flawed arguments

Wiktionary

論辯時，因為理由或準備的材料不充分，以致於無言以對。

重編國語辭典

Entry Composition

1 詞 cí
  1. word
  2. statement; speech; lyrics

classifier: 首
2 窮 qióng
  1. poor
  2. destitute
  3. to use up
  4. to exhaust
  5. thoroughly
  6. extremely
  7. (coll.) persistently and pointlessly

Containing this entry

理屈詞窮 lǐqūcíqióng
  1. lit. having presented a flawed argument, one has nothing further to add (idiom)
  2. fig. unable to provide a convincing argument to support one's position
  3. to not have a leg to stand on
詞窮理屈 cíqiónglǐqū