Simply, practically: 简直
副词 / adverbs
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
Subject + 简直 + (是) + exaggeration
简直 (jiǎnzhí) = "simply, practically, downright". It introduces an exaggeration to express a strong feeling (surprise, admiration, anger): 这个价格简直太贵了！
Often combined with 太……了, 是, 像……一样, or a strong negative (简直不敢相信 = can hardly believe it).
It's an emotional word: don't use it for neutral statements.
Examples
这里的房价简直太高了！
Zhèlǐ de fángjià jiǎnzhí tài gāo le!House prices here are just ridiculous!
我简直不敢相信，我中奖了！
Wǒ jiǎnzhí bù gǎn xiāngxìn, wǒ zhòngjiǎng le!I can hardly believe it: I've won!
他花钱简直像流水一样。
Tā huā qián jiǎnzhí xiàng liúshuǐ yíyàng.He spends money like water.
Common mistakes
✗ 今天简直是星期一。 → no exaggeration, just a fact. ✓ 今天是星期一。
✗ 简直很好 → prefer 简直太好了。