It is not the Economics but the Vocabulary

Today I gave one of my midterms. The midterm contained Multiple choice questions, Short answers and Graphing problems. My multiple choice questions come from the text book publishers. The students tend to read the textbook if they know the questions are written by the author. Also I find it difficult to create the wrong answers for multiple choice questions. Before using any question I go through and edit them for accuracy. I create my own short answer and graphing questions based on what was covered in class.
I had known that some students have difficulty with the English language, but I did not know the extent. Today a few students asked me the meaning of the following words:

zeal

unexpected

(they knew expected, it was the Un that confused them!)

ambiguous

repeal

and the one that really hurt my feelings:

Dismal

Note: My English grammar is not that great either.