a painful topic; a sore subject; secrets (/problems) one doesn’t want to reveal; sth. which it would be awkward to disclose;sth embarrassing to mention ❍ 他那家庭之中，总有许多～的； …… (吴趼人《二十年目睹之怪现状》七十七) In his family there is always something embarrassing to mention.
难言之隐
unmentionable secret; sth difficult to express or awkward to disclose
难言之隐nán yán zhī yǐn
隐：隐情。难以说出来的事情或原因。a painful topic, sth. embarrassing to mention, a sore subject, sth. difficult to express