What is a vegetable?

According to the book "Mostly Vegetables"

The primary definition for vegetable is simple "a plant". but then what about fruits?  Are some foods vegetables and fruits at the same time?  Well, it depends on who's talking.  Botanists say a fruit is anything that derives from a flower's ovary and contains one or more seeds.  According to this definition, many vegetables shift over to the fruit tribe.  Here are some examples of botanical fruits that are culinary vegetables:
Costner, Susan. (1996). Mostly Vegetables. New York, NY: Bantam Dell Pub Group.