Growing up - we ate breakfast, lunch, and supper every day - "Dinner" was saved for eating out, eating at other people's houses, or the BIG meal (Sunday dinner was after church around 1 pm - Thanksgiving, Christmas, or Easter dinners might be any time between 1 and 3 pm with a later meal prepared from leftovers about the time of the usual "supper").
Today - dinner & supper get used interchangeably while I am fixing the evening meal - even if it is a ham & cheese omelette (usually served for a combination breakfast/lunch on weekends around our house)!