Description
Ardency is the warm, active effort to choose what is skillful and abandon what is not, rather than passively sitting back and watching. Thanissaro Bhikkhu uses the word to render the Pali ātāpī.
Tapas and ātāpī both come from √tap, to burn. The English word ardent comes from Latin ardēre, also to burn. So the heat is in all three words.