however

but, however, still, yet, nevertheless, while, whereas

这些连词或副词均含“但是，可是，然而，而”之意。
but: 口语常用词，语气较强，泛指与前述情况相反。
however: 表转折关系，语气稍弱于but，连接性也弱一些，因而常作插入语。
still: 语气强，多用于肯定句或疑问句。指尽管作出让步，采取措施或表示反对，但情况仍然如故，无所改变。
yet: 常用于否定句，语气比still稍强。指不管作出多大努力或让步，仍达不到预期的结果。
nevertheless: 指尽管作出完全让步，也不会发生任何影响。
while: 表对比，一般可与whereas换用，但程度弱一些。
whereas: 表对比，一般可与while互换。

but, however

这两个连词都有“但是，可是，然而”之意。
but: 连接两个分句或有关部分，表示转折或逻辑上的对比关系，使用最广，口语中更为常见。

• we love peace but we are not afraid of war.
  我们热爱和平，但我们并不害怕战争。

however: 转折意味比but弱，连接的两个分句或有关部分的关系较为松弛，后一部分常起附带说明或衬托作用。however常以插入语形式出现在句子中间，前后用逗号隔开，也可置于句首或句末。

• later，however，he decided to go.
  可是后来他决定去了。

副词 however:

1. despite anything to the contrary (usually following a concession)
   同义词：nevertheless, withal, still, yet, all the same, even so, nonetheless, notwithstanding
2. by contrast; on the other hand
3. to whatever degree or extent
4. in whatever way or manner

1. She felt ill. She went to work, however, and tried to concentrate.
   她病了。然而她照旧去上班，并且尽力集中精神工作。
2. His first response was to say no. Later, however, he changed his mind.
   他最初的反应是不同意。可是後来他改变了主意。
3. However does he manage to write music when he is so deaf?
   他聋成这个样子，究竟是怎样从事作曲的呢？
4. I thought those figures were correct. However, I have recently heard they were not.
   我原以为那些数字正确无误。不过我最近听说并不正确。
5. In one's own home, one can act however one wishes.
   一个人在自己家里，可以爱怎么做就怎么做。
6. We must do good rather than evil, on however humble a scale.
   勿因善小而不为，勿因恶小而为之。

how.ev.er

adv.（副词）
In whatever manner or way:
无论如何，不管怎样：
例句：
However he did it, it was very clever.
不管他是怎么做的，他做得很聪明

To whatever degree or extent:
任何都：无论程度、广度如何：
例句：
.have begun, however reluctantly, to acknowledge the legitimacy of some of the concerns.(Christopher Lasch)
.无论多么地不情愿，…已开始承认有些担忧是有其合理性的.(克里斯托弗·拉希)

In what way. Used as an intensive ofhow :
怎样。用作how 的加强语气词：
例句：
However did you get here so soonô
你怎么会这么快赶来的ô

In spite of that; nevertheless; yet:
尽管；然而；还是：
例句：
The book is expensive; however, it`s worth it.
这本书很贵；却很值

On the other hand; by contrast:
另一方面；比较而言：
例句：
The first part was easy; the second, however, took hours.
第一部分很简单；比较而言，第二部分就要费力了

conj.（连接词）
In whatever manner or way:
不管用什么方法：
例句：
Dress however you like.
你喜欢怎么穿就怎么穿

Archaic Notwithstanding that; although.
【古语】 尽管；虽然

Although some grammarians have insisted thathowever should not be used to begin a sentence, this rule has been ignored by a number of reputable writers.See Usage Note at but ,whatever
虽然有些语法学家坚持认为however 不应用在句首， 但有相当一部分知名作家不理会这条规则参见 but,whatever