Definitions
1.nounA strand of yarn etc. as used to guide one through a labyrinth; something which points the way, a guide.
2.nounInformation which may lead one to a certain point or conclusion.
3.nounAn object or a kind of indication which may be used as evidence.
4.nounInsight or understanding ("to have a clue [about]" or "to have clue". See have a clue, clue stick)
5.verbTo provide with a clue."The crossword compiler wasn't sure how to clue the word "should"."
6.verbTo provide someone with information which he or she lacks (often used with "in" or "up")."Smith, clue Jones in on what's been happening."