ἑκών

Romans 8:20 ἑκοῦσα willingly

For the creation was subjected to futility, not by its own will, but because of the One who subjected it, in hope

1 Corinthians 9:17 ἑκὼν willingly

If my preaching is voluntary, I have a reward. But if it is not voluntary, I am still entrusted with a responsibility.