表语是说明主语是什么或主语怎么样,与系动词一起构成系表结构,
eg.I am a doctor（doctor表语）. The food tastes nice（nice表语）.
定语是起修饰限定的成分--修饰某一名词或代词的词或从句（定语从句）. It is an interesting(interesting定语修饰book) book.
It is the book that I bought yesterday.(that I bought yesterday定语从句修饰book).
希望对你有帮助,望采纳.