Synonyms: elusive, tough, baffling, problematic, problematical, knotty
Definition: making great mental demands; hard to comprehend or solve or believe
Usage: a baffling problem; I faced the knotty problem of what to have for breakfast; a problematic situation at home
Similar words: difficult, hard
Definition: not easy; requiring great physical or mental effort to accomplish or comprehend or endure
Usage: a difficult task; nesting places on the cliffs are difficult of access; difficult times; why is it so hard for you to keep a secret?