Stiff
Hard, Firm
い adjective
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of stiff? It's stiff, hard, or firm.
The reading is the same as a very similar word, 固い. So, if you can use that word to help you to remember, you'll remember the reading of this word in no time as well!
彼の筋肉は、岩のように硬い。
His muscles are as firm as rock.
新人モデルは、緊張で表情が少し硬くなっていた。
The new model's expression was a little stiff with nervousness.
ダイヤモンドよりも硬い石があることは、ご存知ですか？
Did you know that there are stones that are harder than diamonds?