Though the task is laborious, the workers still find time to relax. - Antonym: Antonimos are words that have the opposite meaning. In that sentence we have the statement that the workers had time to relax, even with laborious work, we can see that relaxing is the antonym of "laborious."
The wild horse is docile; it allows them to pet its nose, feed it carrots, and stroke its belly. - Explanation: The sentence presented after the word "docile" explains it, showing that the animal, even though it is wild, allows it to be petted and fed by humans.
The dancer is flexible and lithe in her movements. - synoym: unlike antonimo, the synonym has two words that have the same meaning and do not impose a concept of duality in the sentence. In this sentence the words "flexible" and "lithe" are synonymous.
The author Mary Shelley use the word chimerical in that line because she said that the powers of Cornelius Agrippa were improbable and because she wanted to say this in a fancy way.
Hope this Helps :)
BTW, Mary Shelley is the author of Frankenstein <span />