butt rot /b@t rät/ n. a fungal disease affecting the butt, or base, of a tree bot•tom gas /bä2-t@m gas/ n. a type of breathing gas carried in portable tanks and inhaled by under-water divers   The English language is full of words that sound obscene but aren’t. Words like arsole (an organic chemical compound), crack spread (a calculation showing theoretical market values of petroleum), cunctator (a person who procrastinates, delays, or wastes time), and spotted dick (a traditional English dessert made with hot, thick custard).   Seventh-grade English teacher Eric Groves, Sr., has spent years listening to his students giggle after he used terms like thespian, coccyx, and masticate. Now he has compiled hundreds of these so-called “dirty” words into a delightful glossary, complete with illustrated definitions of their true meanings. From air cock (a valve on a boiler) and bushmaster (a large venomous snake) to cummingtonite (a mineral) and beyond, Butt Rot and Bottom Gas is a hilarious reference for word lovers and the snickering seventh grader in all of us.