Hard

困難 /困难

kùnnan

(requiring a lot of effort to do or understand)

硬

yìng

(resistant to pressure)

艱難 /艰难

jiānnán

(demanding a lot of effort to endure)

難 /难

nán

(requiring a lot of effort to do or understand)

努力

nǔlì

(with much force or effort (related to act of think))

認真 /认真

rènzhēn

(with much force or effort (related to act of think))