Synonyms: Most cryptic clues involve knowing the synonyms of some word that is part of the clue. Often the synonym is on the secondary or tertiary meaning of the word in the clue, not the primary meaning. For example, a clue may contain the word "contract".
Similarly, general-knowledge puzzles usually contain clues to which the solver either knows the answer, or does not: for example, 1973 FA Cup winners (10). Cryptic-crossword clues are written in code, and solvers need to understand how to recognise which type of code has been used, in order to unscramble them.