A simile is a device of figurative language in which a comparison is made between two things using the words "like" or "as."
The following are a few examples of similes in Tuck Everlasting:
"Jesse was like water, quick and thin."
Here, Jesse Tuck is being compared to water to describe his appearance and personality. This is a particularly interesting comparison given the fact that Jesse's youth and appearance are kept intact by the fact that he consumes the water that gives everlasting life.
"If people knowed about the spring down there in Treegap, they'd all come running like pigs to slops."
Here, the people who would potentially find out about the spring water are compared to pigs who are eager to consume their dinner. In other words, the people would be uncontrollable and in a terrible mess to suck up this strange and potentially dangerous resource.
"Mae swung the shotgun round her head like a wheel."
Here, Mae's gun is being compared to a wheel to indicate the circular motion in which she is moving it. This helps illustrate the motion more clearly.