1. A large controlled outdoor fire, usually made from bales of straw or wood.
2. A social event that takes place near the mentioned fire.
The word is believed to be a corruption of "bone fire" deriving from a Celtic midsummer festival where animal bones were burnt to ward off evil spirits.
1. I helped my dad prepare a bonfire and i burned my new pants.
2. You should have been at Mike's bonfire last week, we got really drunk.