An ink, invisible on application or soon thereafter, that can later be rendered visible by some process, such as exposing it to heat. / An ink used in pranks that is visible at first but soon disap...

(linguistics) In violation of one or more of the rules and conventions of a language as defined by the grammar, resulting in unacceptable or incorrect usage.

One who navigates a hoy (sailing vessel).

(initialism) per cent mille (1000 pcm = 1%)