wart

wart n.  A small, {crock}y {feature} that sticks out
   of an otherwise {clean} design.  Something conspicuous for
   localized ugliness, especially a special-case exception to a
   general rule.  For example, in some versions of `csh(1)',
   single quotes literalize every character inside them except
   `!'.  In ANSI C, the `??' syntax used for obtaining ASCII
   characters in a foreign environment is a wart.  See also
   {miswart}.