More unyielding

• Less cushiony
• Higher on the Mohs scale
• More challenging
• More puzzling, as a crossword
• Less lenient
• More demanding
• Taking more time, probably, as a test

WordNet Word definitions in WordNet
adv. with 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" with firmness; "held hard to the railing" [syn: firmly ] earnestly or intently; "thought hard about ...

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Harder \Har"der\ (h[aum]r"d[~e]r), n. (Zo["o]l.) A South African mullet, salted for food.