说话或写文章不能准确地表达意思to be unable to express one’s meaning in words

• 不少战士一到正式发言就抓耳挠腮、词不达意。

  When they have to make a speech, quite some number of soldiers just scratch their heads, unable to convey what they want to say in words.

• 他作诗写文喜欢用些华丽的辞藻，可是往往词不达意。

  He likes to use purple prose in his writing, but it can’t accurately convey his meaning.