The word "wibble-wobble" is often used to describe a shaky or unsteady movement. However, there are a number of synonyms that can be used to convey a similar meaning. "Quiver" is a good option for describing a slight tremble or shake. "Tremble" suggests a more pronounced shaking or vibrating movement. "Shimmer" can be used to describe a wavy or unsteady appearance. "Waver" is another good synonym, suggesting a wavering or unsteady movement. "Shudder" conveys a sense of a sudden and intense shake. "Jiggle" is a more playful or casual way of describing a slight shaking or movement. Whatever word you choose, there are plenty of options for describing wibble-wobble.