infirm

To contradict, to provide proof that something is not.

"The thought is that you see an episode of observation, experiment, or reasoning as confirming or infirming a hypothesis depending on whether your probability for it increases or decreases during the episode."

Weak or ill, not in good health.

"He was infirm of body but still keen of mind, and though it looked like he couldn't walk across the room, he crushed me in debate."

Irresolute; weak of mind or will.

Frail; unstable; insecure.