[tlhIngan Hol] Is idiom the same as slang ?

A little bird told me, that HQ 12.3 p.9 sept 2003, lists Soj as "matter, concern, affair". And it says, it is an idiomatic meaning of the word Soj "food, drink". Now, since the HQ transcription project went down the toilet, I don't know the exact passage I'm referring to, but I wonder.. Saying that this is "an idiomatic meaning of Soj", is the same as saying "it is a slang meaning" ? Is there a difference between an idiomatic  use of a word and a slang word ? ~ m. qunen'oS have you ever heard of the tragedy of him who refused to adhere to ca'non ?