A fork of Rural Dictionary
It means to hang out and chill and do some sort of activity that does not require too much effort. Usually used in reference to doing drugs or taking mind/body altering substances, but does not have to be used in that content necessarily.
Mike: Hey John, come tone with us for a bit. We are just watching some South Park. Bryan: Hey man wanna come tone down a bit with me and Paul? (In reference to marijuana) Joe: Nah man I can't be tonin when I got an 8 am test tomorrow.