硬(yìng) - hard, stiff, firm in Mandarin

硬 (yìng) is hardness you can feel with a finger or a tooth. A mattress, a biscuit, a road surface, a boiled egg: if it resists pressure, it is 硬. Its everyday opposite is 软 (ruǎn, soft).

The word stretches easily into character. 态度很硬 is a firm, unyielding attitude, and 硬撑 is gritting your teeth and carrying on when you should stop. Used before a verb, 硬 carries the sense of doing something in the teeth of resistance: 硬要 is insisting, 硬说 is claiming something flatly despite the evidence.

The trap for English speakers is that our word "hard" does two jobs and 硬 only does one. A hard exam, a hard question, a hard day at work are all 难 (nán), never 硬. Say 这个问题很硬 and you have described the physical texture of the question, which is not what you meant.