Acrophobia is a noun that refers to a fear of heights. 

The Greek word akron (AK ron) means ‘summit,’ while the Greek suffix P-H-O-B-I-A means fear. Since the late 19th century people terrified of high places have used our word of the day to describe their condition. Here’s an example:

Tammy has such gripping acrophobia that she won’t date a man over six feet tall. She’s afraid that just reaching up to give him a kiss will make her dizzy.