(adj): requiring full use of your abilities or resources
(adj): difficult to accomplish; demanding considerable mental effort and skill
(adj): hard to deal with; especially causing pain or embarrassment
(adj): making great mental demands; hard to comprehend or solve or believe
(adj): having concealed difficulty
(adj): difficult to handle; requiring great tact
(adj): unpredictably difficult in operation; likely to be troublesome
(adj): requiring great effort
(adj): extremely difficult; requiring the strength of a Hercules
(adj): exasperatingly difficult to handle or circumvent
(adj): full of hardship or trials
(adj): very difficult; severely testing stamina or resolution
(adj): requiring effort or concentration; complex and not easy to answer or solve
(adj): prenominal) -- (impressively difficult
(adj): bristling with perplexities
(adj): difficult to deal with
(adj): hard to endure
(adj): causing difficulty in finding an answer or solution; much disputed
(adj): vs. manageable), difficult -- (hard to control
(adj): of persons
(adj): incapable of being checked or restrained
