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，總有許多～的； …… (吳趼人《二十年目睹之怪現(xiàn)狀》七十七) In his family there is always something embarrassing to mention.
難言之隱
unmentionable secret; sth difficult to express or awkward to disclose
難言之隱nán yán zhī yǐn
隱：隱情。難以說出來的事情或原因。a painful topic, sth. embarrassing to mention, a sore subject, sth. difficult to express