>Without looking into dictionary, just from the common usage, I gather that abuse is mistreatment, torture, or any other harm done to someone.
>
>Now what does one need to do to a substance to make this deed fall into category of "substance abuse". Does one flog a beer? Force a joint into solitary confinement at -20?

I agree - it's a silly expression. People don't even "misuse" (a more apt word) drugs, as they get exactly the use out of them that they intended. e.g if you smoke a spliff it's not as if you should have been rubbing it on a cut on your knee!