这几个词的词义都含有：不合法之意，但是用法和含义有差别：
1.illegal adj. 违法的
指法律禁止的。反义词：legal
I have never taken illegal drugs.
我从未使用过违禁药品。
This is a list of illegal drugs.
这是一张列有违禁药品的单子。
The illegal trade in animal products continues to flourish
野生动物制品的非法交易仍旧猖獗。
I could provide you with the addresses of at least three illegal drinking dens.
我可以为你提供至少3处非法饮酒窝点的地址。
Both women had hired illegal aliens for child care
两个女人都曾雇过非法入境者照看孩子。
Birth control was illegal there until 1978
1978年以前那里节育是非法的。
Bylaws are to make it illegal to smoke in public.
地方法规将规定在公共场合抽烟为非法。
The bylaw makes it illegal to drink in certain areas.
当地的地方法规规定在特定区域饮酒属于非法。
It is illegal to scalp train tickets.
倒卖火车票是违法的。
It is illegal to intercept radio messages.
拦截无线电报是非法的。
It's illegal to drive through a red light.
开车闯红灯是违章行为。
It is illegal to reproduce these worksheets without permission from the publisher.
未经出版者许可翻印这些习题是违法的。
Since 1977 otter hunting has been illegal.
捕猎水獭1977年以后就被列为非法了。
It is illegal to sell cigarettes to children who are under age.
售香烟给未到法定年龄的儿童是非法的。
It is illegal to have sex with a person under the age of 16.
和16岁以下的未成年人发生性行为是违法的。
There was no suggestion that he was doing anything illegal.
说他在从事非法活动无任何根据。
Despite his illegal act, few people think badly of him.
尽管他干了违法的事情，但很少有人认为他不好。
They have persistently denied claims of illegal dealing.
他们一再否认进行非法交易的说法。
The illegal payments were discovered by a journalist working undercover.
这些非法付款是一位暗中查访的新闻记者发现的。
He fronted for them in several illegal property deals.
他为他们在几次非法房地产交易中作了掩护。
Illegal immigrants were given the opportunity to regularize their position.
非法移民得到了使其身份合法化的机会。
We in this party will have no truck with illegal organizations.
我们党的成员绝不与非法组织有来往。
He entered the country illegally.
他通过非法途径进入了这个国家。
They were yesterday convicted of illegally using a handgun...
他们昨天被判犯有非法使用手枪罪。
The previous government had acted illegally.
上届政府采取的行动不合法。
He surmised that he had discovered one of the illegal streets.
他推测自己已经发现了一条非法活动猖獗的街道。
The police ran a sting operation to crack down on illegal guns.
警方展开诱捕行动以严打非法枪支。
2.illegitimate /ˌɪləˈdʒɪtəmət/ adj. 不合规则的，不合理的，非法的；私生的；非婚生的；
指不符合相关协议或规定的。反义词：legitimate
在涵义：不合法的；非法律认可的；非法定的之意时与.illegal用法重合。
illegitimate trade
非法贸易
The election was dismissed as illegitimate by the opposition...
反对党以不合法为由拒绝接受选举结果。
He was criticized for his illegitimate use of public funds.
他因非法使用公共资金而遭到批评。
We only married in order that the child should be legitimate.
我们结婚纯粹是为了给孩子一个合法身份。
His business operations are perfectly legitimate.
他的商业活动完全合法。
The government will not seek to disrupt the legitimate business activities of the defendant.
政府无意干扰被告的合法经营活动。
The empire could not cohere as a legitimate whole.
这个帝国无法凝聚成一个合法的整体。
Most doctors appear to recognize homeopathy as a legitimate form of medicine
大多数医生似乎都接受顺势疗法是一种合理的医疗手段。
They had a legitimate grievance
他们的抱怨是合乎情理的。
The threat of bankruptcy is a legitimate tool to extract money from them.
破产威胁是从他们那里索得钱款的合法手段。
Is his business strictly illegitimate?
他的生意是否绝对非法？
It seemed a perfectly legitimate question.
这似乎是完全合乎情理的问题。
That's a perfectly legitimate fear.
怀有这种恐惧完全在情理之中。
The French government has condemned the coup in Haiti and has demanded the restoration of the legitimate government...
法国政府对海地政变表示谴责，并要求恢复合法政府的地位。
3.illicit adj. 非法的；违法的；不正当的；社会不容许的；违背社会常规的
指违反法律法规或为社会所不能接受的。反义词：licit
Anyone who sells illicit drugs will be punished.
任何人出售违禁药品都会被处罚。
The crime elicited an outcry against illicit drugs.
那起罪行引发了打击违禁药品的呼声。
The illicit love affair should end immediately.
应马上结束这种不正当的男女关系。
Dante clearly condemns illicit love.
丹蒂旗帜鲜明地谴责不正当恋情。