Crux and Whodunit

Crux noun - The central part or aspect of something under consideration.

Whodunit and crux are semantically related In some cases you can use "Whodunit" instead a noun "Crux".

Whodunit noun - A story about a crime (usually murder) presented as a novel or play or movie.

Crux and whodunit are semantically related in puzzle topic. Sometimes you can use "Crux" instead a noun "Whodunit", if it concerns topics such as mystery.