Opium is a tar-like drug, most often black in color. It tastes like no other, being made from poppies. It makes you feel like you're floating, yet sinking into your couch. It's amazing: afterall, there was a war over opium...
"My mouth tastes like flowers. I must have smoked some opium."
A piece is a one of a kind work of art, made of blown glass, that you can smoke pot out of. "Piece" is also an acceptable word when at a head shop and trying not to get kicked out. "Water pipe" would also be acceptable.
Ganja smoking device examples:
"Let's pack up my new piece and get stoned off our asses!"