The antonyms for the word "infallible" are fallible, erring, imperfect, faulty, flawed, and unreliable. These words may be used to describe something or someone that is subject to making mistakes or cannot be fully trusted. Fallible refers to something that is likely to be wrong or mistaken. Erring means having made a mistake or committed a fault. Imperfect describes something that is not perfect or complete. Faulty implies that something is defective or has a flaw. Flawed means that something has a defect or imperfection. Unreliable refers to something that cannot be relied on or trusted completely.