Welcome, val. I ran *gesis through Onelook, and it's not that. Though the religious ref.'s made me think of the word sinning, but I can't imagine that's what you're looking for. (And running sin through the thesaurus didn't work, either.)

Then I tried *esis...and there are so many that I'm going to ask you to check the list yourself. Sorry I couldn't be of help. Though perhaps tsuwm might know off the top of his head.