Etymology

• Colloquial butty (1802), meaning companion, also the form of an older dialect term meaning workmate, associated with coalmining. Itself believed derived from booty fellow (1530), a partner with whom one shares booty or loot. http://www.etymonline.com/index.php?term=buddy

• Sometimes referred to in North American dictionaries as an alteration of brother.

Noun

1. A friend or casual acquaintance.

   They have been buddies since they were in school.

2. A partner for a particular activity.

   drinking buddies

3. An informal address to a stranger; a placeholder name for a person one does not know.

   Hey, buddy, I think you dropped this.

Verb

1. To assign a buddy, or partner.