A piece of neckware that is supposed to simulate an undershirt, so that one only has to wear the dickie and an overshirt. Were very popular in the sixties, due to the Beatle's use of them. They were mostly starched and bleached, and meant to look like a sweatshirt. The Beatles used them so they wouldn't overheat while performing, but could still look dressed up.
I thought my Starfleet uniform came with one of those cool blue undershirts, but all I got was dickie.
At Phillips Exeter Academy, in lieu of detention, for skipping a class, something known as a dickie is given, which has no real effect until three are accumulated, at which point one is punished with early curfew and suspended priviledges.
Supposedly from an old headmaster known for giving out a good deal of punishments.
When I skipped my English class, I managed to get out of getting a dickie by telling my teacher I was in the health center sleeping even though I was actually watching a movie with my buddies in the common room.