chuck·le 
(chŭkəl)
(chŭkəl)intr.v. chuck·led, chuck·ling, chuck·les
1. To laugh quietly or to oneself.
2. To cluck or chuck, as a hen.
n.
A quiet laugh of mild amusement or satisfaction.
[ Probably frequentative of CHUCK3.]
chuckler n.
chuckle·some adj.
chuckling·ly (-lĭng-lē) adv.