unfit, unhealthy, unwell, ailing, ill, bad, diseased, poorly, sick, sickly, upset 与 run-down 这些词均可表示“不健康的，生病的”，但在词义或用法上有所区别。
(1) unfit指“不健康的，虚弱的”，可指身体或精神两方面。
- He is pretty unfit . He needs medical treatment and a lot more exercise.
他体质相当弱，需要药物治疗和多锻炼身体。 - In my present unfit state, I can't make the travel now.
以我现在的虚弱状态，我无法去旅行。
(2) ①unhealthy意为“身体不好的，不健康的，显出病态的”，可指身体或精神长时间状况不佳或经常患病。
- Because of the years of war, the children are unhealthy for lack of good food.
由于多年的战争，孩子们因缺少良好的食物而健康状况欠佳。 - Her skin is in unhealthy greenish color.
她的皮肤呈病态的青色。
②unhealthy还表示“对健康不利的”。
- They are working in crowded unhealthy conditions.
他们在拥挤的不健康的环境中工作。 - The recent hot wet climate is very unhealthy .
近来的潮热天气对健康非常不利。
③unhealthy又作“不利身心健康的，不正常的”解。
- A home where the parents fight constantly is an unhealthy environment for a child.
一个父母经常打架的家庭对孩子来说是一个不利身心健康的环境。
(3) unwell指“身体欠佳，特别是短时间不适”。
- I was unwell this morning, but I'm fine again now.
今天早晨我感觉身体不适，但现在又好了。 - Mary is unwell , so I've sent her to bed and called the doctor.
玛丽感觉不舒服，于是我让她上床并叫来了医生。
(4) ailing指“生病的，健康不佳的”，尤指在较长时间患有不是很严重的疾病，是非正式用语。
- He's an old man now and has been ailing for a long time.
他现在已是一位老人，病了很长时间了。
(5) ①ill意为“生病，身体不适”，可指突然的、短时间的患病，也可指较长时间的生病。另外，ill一般不用在名词前作定语，而用sick，但偶尔也有例外，如：an ill name/deed/omen/temper/repute/luck/will, ill comments/effects, 这时，ill 的意思是“坏的，不良的，恶劣的”。
- She has been ill for about two weeks.
她已病了大约两周。 - I felt ill this morning, but I'm OK now.
今天早晨我感觉不适，但现在好了。 - He was taken ill with a cold on the plane from Moscow to Beijing.
在从莫斯科到北京的飞机上他因感冒而感到不适。
②ill偶尔也指“受伤”。
- One week after the battle, two armed policemen were still seriously ill in hospital.
在这次战斗后的一星期，两名武警仍因重伤而躺在医院。
(6) ①bad可作“不舒服，有毛病的”解。
- He's got a bad heart and can't climb mountains.
他心脏不好，不能爬山。 - My eyes have been somewhat bad of late.
我的眼睛最近有点不舒服。 - I felt rather bad this morning.
今天早晨我感觉相当不舒服。
②be taken bad意为“生病了”，与be taken ill/sick意思相同。
- He was taken bad yesterday, so he didn't come to the meeting.
他昨天病了，所以没来开会。
③bad也可表示“对……有害或不利”。
- Smoking is certainly very bad for the throat.
抽烟当然对咽喉极为有害。 - Don't read in the dim light. It's bad for your eyes.
不要在昏暗的光线中读书，那对你的眼睛不好。
(7) diseased意为“有病的，为疾病伤害的”，可用于人的器官，也可用于动植物。
- The doctor discovered that his liver was diseased .
医生发现他的肝脏已经病变。 - He rooted the diseased plants out in his garden.
他把园中有病害的植物除掉了。
(8) poorly可作“身体不适”解，是非正式用语，主要用于英式英语。
- I've been poorly recently.
最近我的身体不好。 - I felt very poorly this morning.
今天早晨我感到非常不适。
(9) ①sick也可作“生病，不适”解，在英式英语中常用ill, unwell，在美式英语中常用sick。
- He was off sick with a bad cold for a week.
他因重感冒已休假了一周。 - He got sick with a cold last week.
他上周患了感冒。 - She had to stay at home to look after her sick mother.
她必须待在家里照顾她生病的母亲。
②sick还可作“恶心”解。
- I feel sick , it must be something I ate.
我感到恶心，肯定是我吃的东西的问题。
(10) ①sickly可指“多病的，有病的”。
- What a sickly child she is. She's constantly catching colds.
她真是个多病的孩子，她经常感冒。 - Did you notice his sickly complexion?
你注意到他的病容了吗？ - These plants look rather sickly .
这些植物看上去像害了大病一般。
②sickly还可作“使人生病的，令人厌恶的”解。
- That damn factory is always sending out a sickly smell.
那家讨厌的工厂总是散发出使人厌恶的气味。 - In the flood-stricken areas, the people are living in sickly conditions.
在洪涝灾区，人们生活在不利健康的环境中。
(11) upset是过去分词用作形容词，可指“不舒服，难受”，一般程度较轻，多指胃部。
- I've been suffering from an upset stomach lately.
最近我一直饱受胃疼的困扰。 - The child has an upset stomach.
这个孩子胃不舒服。 - My stomach was upset for days after that party.
那次宴会之后，我的胃难受了好几天。
(12) run-down用于口语，可作“虚弱，疲乏，健康不佳”解。
- She is still quite run-down after the operation.
手术后她仍相当虚弱。 - I need a rest. I feel rather run-down .
我需要休息一下，我感到非常疲乏。
