From The Collaborative International Dictionary of English v.0.48 :
chummy \chummy\ adj.
1. having the relationship of friends or pals. [colloquial]
Syn: matey, pally, palsy-walsy.
[WordNet 1.5]
2. associated on close terms. [informal]
Syn: thick(predicate).
[WordNet 1.5]
From WordNet (r) 3.0 (2006) :
chummy
adj 1: (used colloquially) having the relationship of friends or
pals [syn: chummy, matey, pally, palsy-walsy]
2: (used informally) associated on close terms; "a close
friend"; "the bartender was chummy with the regular
customers"; "the two were thick as thieves for months" [syn:
chummy, buddy-buddy, thick(p)]