infirm UK /ɪnˈfɜːm/US /ɪnˈfɜɹm/adjective 3verb 1forms 5 adjective3 •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. •Frail; unstable; insecure.He who fixes upon false Principles, treads upon Infirm ground, and so sinks […] — 1692 •Irresolute; weak of mind or will.Infirm of purpose! Give me the daggers: […] — 1606 verb1 •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 the probability of it being correct increases or decreases during the episode. formsinfirmed · infirming · infirms · infirmer · infirmest