1a piece of evidence or information used in the detection of a crime or solving of a mystery:police officers are still searching for clues
a fact or idea that serves as a guide or aid in a task or problem:archaeological evidence can give clues about the past
2a verbal formula giving an indication as to what is to be inserted in a particular space in a crossword or other puzzle.
verb (clues, clueing, clued)
[with object] (clue someone in) informal
inform someone about a particular matter:Stella had clued her in about Peter
not have a clue
informal know nothing about something or about how to do something.
late Middle English: variant of clew. The original sense was 'a ball of thread'; hence one used to guide a person out of a labyrinth (literally or figuratively). sense 1 of the noun dates from the early 17th century