When I use a word . . . Medical Janus words

A Janus word or phrase has two meanings, each the opposite of the other. Janus words are named after the two-faced Roman god of archways and doors, Janus. There are many such words in English, the classical example being “cleave,” which means to divide or to unite, coming as it does from two different Old English words, cleofan and clifian. However, there are relatively few medical Janus words, which may be just as well, since ambiguity should be avoided whenever possible.