(a)difficult, hardnot easy; requiring great physical or mental effort to accomplish or comprehend or endure“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?”
(a)hard(of speech sounds); produced with the back of the tongue raised toward or touching the velum“Russian distinguished between hard consonants and palatalized or soft consonants”
(s)arduous, backbreaking, grueling, gruelling, hard, heavy, laborious, operose, punishing, toilsomecharacterized by effort to the point of exhaustion; especially physical effort“worked their arduous way up the mining valley”, “a grueling campaign”, “hard labor”, “heavy work”, “heavy going”, “spent many laborious hours on the project”, “set a punishing pace”
(r)hardwith effort or force or vigor“the team played hard”, “worked hard all day”, “pressed hard on the lever”, “hit the ball hard”, “slammed the door hard”
(r)hardvery near or close in space or time“it stands hard by the railroad tracks”, “they were hard on his heels”, “a strike followed hard upon the plant's opening”