inflexible, rigid, compressed, compact, dense, resisting, adamantine, flinty. See firm1
toilsome, burdensome, wearisome, exhausting. Hard, difficult both describe something resistant to one's efforts or one's endurance. Hard is the general word: hard times; It was hard to endure the severe weather.
Difficult means not easy, and particularly denotes that which requires special effort or skill: a difficult task. 5.
complex, complicated, perplexing, puzzling, intricate, knotty, tough. 6.
arduous, onerous, laborious. 8.
stormy, tempestuous. 10.
severe, rigorous, grinding, cruel, merciless, unsparing. 12.
stern, austere, strict, exacting, relentless, obdurate, adamant; unyielding, unpitying. Hard, callous, unfeeling, unsympathetic imply a lack of interest in, feeling for, or sympathy with others. Hard implies insensibility, either natural or acquired, so that the plight of others makes no impression on one: a hard taskmaster.
Callous may mean the same or that one is himself or herself insensitive to hurt as the result of continued repression and indifference: a callous answer; callous to criticism.
Unfeeling implies natural inability to feel with and for others: an unfeeling and thoughtless remark.
Unsympathetic implies an indifference that precludes pity, compassion, or the like: unsympathetic toward distress. 13.