And askually®, the origin of chum #1 isn't as evident as I thought. From Macquarie Dictionary:

chum
noun 1. a mate or friend. --phrase 2. chum up (with), to become friendly with. [17thC British slang; origin unknown]


http://www.macquariedictionary.com.au/p/dictionary/slang-c.html

What say ye, Brits?