Although cucumbers are botanically a fruit, they are a vegetable in the culinary sense, which is why they are listed as such. The same applies to tomatoes, squash and several other foods that are commonly used as vegetables. Believe it or not, there was an actual ruling on this issue in 1883 by the Supreme Court. Part of that ruling clarifies this matter:
“Botanically speaking, tomatoes are the fruit of a vine, just as are cucumbers, squashes, beans, and peas. But in the common language of the people, whether sellers or consumers of provisions, all these are vegetables which are grown in kitchen gardens, and which, whether eaten cooked or raw, are, like potatoes, carrots, parsnips, turnips, beets, cauliflower, cabbage, celery, and lettuce, usually served at dinner in, with, or after the soup, fish, or meats which constitute the principal part of the repast, and not, like fruits generally, as dessert.”
Thank you for bringing to our attention that jicama has been listed as a fruit. It is a root, and is used as a vegetable.