A synonym is a word or phrase that means exactly or nearly the same thing as the original word or phrase. Additionally, it has to be in the same language. For example, reveal is a synonym of show.
An antonym is a word or phrase that means the opposite of the original word. For example shut is the opposite of close.
The following is a list of synonyms for everlasting:
Since your topic indicates that Tuck Everlasting is the novel in question, the best synonyms are the ones that focus on living forever. The Tucks are an immortal family.
The following is a list of antonyms for the word everlasting:
The best place to look for other synonyms and antonyms is a thesaurus. It is kind of like a dictionary, but its main purpose is to provide lists of synonyms and antonyms. You can get access to several good thesauri by going online.