We borrowed regimen straight from Latin, spelling and all—but in Latin, the word simply meant "rule" or "government." In English, it usually refers to a system of rules or guidelines, often for living a healthy life or taking a regular dose of exercise. The Latin regimen derives from another Latin word, the verb regere, which means "to lead straight" or "to rule." If you trace straight back from regere, you'll find that regimen has plenty of lexical kin, including correct, erect, region, rule, and surge. If you are using the training sense of regimen, be careful not to confuse the word with regiment, another regere descendant, which is used for a military unit.