Word: 快 (kuài) clever; sharp (of knives or wits)

冰箱里拿出来的水果刀，又快又冷

bīngxiāng li ná chūlái de shuǐguǒdāo, yòu kuài yòu lěng

a fruit knife from the fridge: both sharp and cold

刀快不怕脖子粗

dāo kuài búpà bózi cū

if the knife is sharp, you needn't fear the neck is thick

快刀不削自己的柄

kuài dāo bù xiāo zìjǐ de bǐng

a sharp knife doesn't whittle its own handle

快刀不磨是块铁

kuài dāo bù mó shì kuài tiě

a sharp knife left unhoned is just a lump of iron

快刀切豆腐,两不沾

kuài dāoqiē dòufu,liǎng bù zhān

a sharp knife cutting tofu: neither side sticks

快刀切豆腐,两面光

kuài dāoqiē dòufu,liǎngmiànguāng

a sharp knife cutting tofu: both faces smooth

斧快不怕木柴硬

fǔ kuài búpà mùchái yìng

if the axe is sharp, hard wood is nothing to fear

瞎子磨刀,快了

xiāzi módāo,kuàile

a blind man sharpening a knife: it's getting sharp / soon

瞎子磨镰刀,快了

xiāzi mó liándāo,kuàile

a blind man sharpening a sickle: nearly sharp

钢刀虽快，不斩无罪之人

gāngdāo suī kuài, bù zhǎn wúzuì zhī rén

though a steel blade is sharp, it does not cut down the innocent