Antonyms of tentative :
Examples of usage:
It was growing dark when a tentative scratch at the door told her of Nick's presence there. "The Keeper of the Door", Ethel M. Dell.
There was a short silence; a tentative civil word from Siward; then Miss Landis took command of something that had a grotesque resemblance to a situation. "The Fighting Chance", Robert W. Chambers.
This selection, he mused, is of course only tentative. "The Haunted Bookshop", Christopher Morley.