smock...
Not just a great word to say, as Hobbes pointed out, it's also a great article of clothing. To expand on Webster1913's definition a bit, a smock can also be a large garment worn over other clothing to prevent their becoming a casualty of art (paint spills, glue smears, crusts of clay, and all that good stuff). A smock is usually pretty shapeless, if only by virtue of its size.
Smocks were mandatory in my elementary school art classes, and as such repeatedly provided an opportunity for my mom to raid my dad's closet and sacrifice whatever shirt of his most offended her sensibilities that year. As a result, my smocks always had a lovely worn-in (and worn-out) feeling to them.
To this day some part of me secretly thinks smocks are the very height of fashion. I'm a huge fan of big, comfy clothes you can wear in layers, and smocks have the added benefit of being utterly stainable. There's something very liberating in knowing you don't have to give a damn about how you look or what gets on you... and besides, anything that brings me back to elementary school art class, where all our works were exuberantly praised for their display of talent or lack thereof, if only for a moment, is ok by me.