Vocabulary Builder Quiz Tool for Students

I teach standard 12th Grade ELA and my students simply don't know enough words. When making tests we constantly have to rewrite questions because they will not know the meaning of half of the words. Yesterday I had a kid ask what "nonsensical" meant. I was nearly at a loss for words. The definition is in the word. They answer questions wrong because they aren't in the simplest of terms. I can tell who was read to as a child and who wasn't based on their vocabulary. I don't know how to catch them up when I am getting them when they are already this far behind. Just needed to vent. Edit: missing apostrophe Update: Thank you to everyone sharing your experiences and giving fantastic advice! I was at a loss and while I knew what solutions may work I wasn't too enthusiastic about implementing the changes. Starting next week I'm taking out my dictionaries and making sure there is one at every table. We will have daily vocabulary warm-ups and weekly vocabulary quizzes. When they don't know a word in a text we can pause to look up the definition. I may look at adding a word wall. Also, to everyone saying that I shouldn't be rewriting test questions in a less than kind manner. Obviously I know that. I was ranting. We need to have a larger conversation in education about how the system and many individuals enable different academic behaviors to the detriment of our students. I am going to change what I was doing. However, I am still allowed to be frustrated that their previous 12 years of education permitted them to reach this point. Again to everyone that gave me kind advice (or admitted when then were being a bit snippy), thank you. You make this profession a kinder and transformative environment.