appamāda: Heedfulness; diligence; zeal. The cornerstone of all skillful mental states, and one of such fundamental import that the Buddha's stressed it in his parting words to his disciples: "All fabrications are subject to decay. Bring about completion by being heedful!" (appamādena sampādetha).
"And what is heedfulness? There is the case where a monk guards his mind with regard to mental fermentation and mental qualities accompanied by fermentation. When his mind is guarded with regard to fermentation and mental qualities accompanied by fermentation, the faculty of conviction goes to the culmination of its development. The faculty of persistence... mindfulness... concentration... discernment goes to the culmination of its development.