Acuity is how sharp a sense or a mind is — how clearly you can think, see, or hear. Doctors talk about visual acuity: how well you can read the letters on the wall chart. You also hear mental acuity, especially about older people: thinking that is still quick and clear, not foggy. Hearing can have acuity too, though that use is less common.

Acuity is how sharp a sense or a mind isacuity 是指一種感官或心智有多敏銳——how clearly you can think, see, or hear你能想得、看得，或聽得多清楚。Doctors talk about visual acuity醫生會講 visual acuity（視敏度）：how well you can read the letters on the wall chart就是你能把牆上視力表的字母讀得多好。You also hear mental acuity你也會聽到 mental acuity（心智敏銳度），especially about older people尤其是講到年長者的時候：thinking that is still quick and clear, not foggy指思考還是又快又清楚，不模糊。Hearing can have acuity too聽力也可以有 acuity，though that use is less common不過這種用法比較少見。

The word is formal. A child would just say “I can see well” or “her mind is still sharp.” Though actually, outside hospitals and careful writing, many English speakers almost only meet it in visual acuity.

The word is formal這個字是正式用語。A child would just say一個小孩就只會說 "I can see well" or "her mind is still sharp.""I can see well"（我看得很清楚）或 "her mind is still sharp"（她的腦筋還是很靈光）。Though actually不過其實，outside hospitals and careful writing在醫院和講究的寫作之外，many English speakers almost only meet it in visual acuity很多英語人士幾乎只會在 visual acuity 這個說法裡遇到它。

It names the sharpness itself, not a clever plan and not a kind personality. It is also not the same as acumen: acuity is how clearly the mind or the senses work; acumen is skill at judging, especially in business.

It names the sharpness itself它指的是敏銳這件事本身，not a clever plan不是指一個聰明的計畫，and not a kind personality也不是指一種和善的個性。It is also not the same as acumen它也跟 acumen 不一樣：acuity is how clearly the mind or the senses workacuity 是心智或感官運作得多清楚；acumen is skill at judging而 acumen 是判斷的能力，especially in business尤其是在商業上。