Bunion: A localized, painful swelling at the base of the big toe due to new bone formation. The affected toe is often curved outward. Bunions are frequently associated with inflammation of the nearby bursa (bursitis) and degenerative joint disease (osteoarthritis). Bunions most commonly affect women, particularly those who wear tight-fitting shoes and high heels. Treatment includes rest, a change in shoes, foot supports, medications, or surgery.