Chancre: The classic painless ulcer of syphilis. The chancre forms in the first (primary) stage of syphilis. It is highly contagious and can last 1-5 weeks. The disease can be transmitted from contact with the ulcer, which is teeming with spirochetes. If the ulcer is outside of the vagina or on the scrotum of the male, the use of condoms may not help in preventing transmission of the disease. Likewise, if the ulcer is in the mouth, merely kissing the infected individual can spread syphilis.