Euphemisms employ substitution of an agreeable or inoffensive expression for one that may offend or suggest something unpleasant.
An idiom is a figure of speech in which the use of a word or words is peculiar to itself in that it has a meaning that usually cannot be derived from the literal meaning of the word or words.
When someone dies, we may say that they “passed away.” We are using a euphemisms to soften the blow of the harsh reality of losing someone. Contrastingly, an idiom is used to heighten the effect. Phrases such as: “kicked the bucket;” “bought the farm;” “assumed room temperature;” or “cashed in their chips” are offensive and are not agreeable but serve a purpose in language.
The Bible makes use euphemisms and idioms.
John 11:11 “Our friend Lazarus has fallen asleep; but I go, so that I may awaken him out of sleep.” Here Jesus uses “sleep” as a euphemism for death. Lazarus had died and Jesus was going to bring him back from the dead.
Jeremiah 23:9 As for the prophets: My heart is broken within me, All my bones tremble; I have become like a drunken man, Even like a man overcome with wine, Because of the Lord And because of His holy words.
Our hearts do not literally break but they feel as if that were true. It is a harsh idiom we use to describe a tough situation.