Take, for example, bridegroom, or groom. In Middle English (ca. 1200-1500), the original term was goom (= man). The extra -r- was added centuries ago by false association with someone who works in a stable to care for horses. America's greatest lexicographer, Noah Webster, fought in vain in the early 19th century to make a man on his wedding day the bridegoom and all his attendants the goomsmen. But the English-speaking people would have none of it - they wanted their extra -r-, and they got it. The harmless mutation survived, and today we're wedded to it.
— Garner's Modern English Usage
by Bryan Garner