Judder refers to a jerky or shaky movement, typically experienced in machines or vehicles. The antonyms for this word would be smooth, steady, or even. Smooth represents a consistent and fluid movement, while steady refers to a motion that is unchanging in its pace and direction. Even denotes a level surface or a lack of unevenness. Usage of these antonyms depends on the context in which the word judder is used. For example, one could say, "the ride was smooth and comfortable, without any judder," or "the machine operated steadily, without any judder or shaking.