stain  
 verb uk/steɪn/ us/steɪn/
  (MARK)            
 C2 [ I or T ]沾污,染污;留下污迹 
to leave a mark on something that is difficult to remove
  Tomato sauce stains terribly - it's really difficult to get it out of clothes. 让番茄酱沾上很麻烦——很难把它从衣服上洗掉。 
 While she was changing the wheel on her car, her coat had become stained with oil. 她给汽车换轮胎时,外套沾上了油污。 
  [ I ]易染污;易着色 
If a material stains, it absorbs substances easily, causing it to become covered with marks, or coloured by a chemical.
  This carpet is ideal for the kitchen because it doesn't stain easily. 这块地毯很适合在厨房里用,因为它很耐脏。 
  [ T ]给…染色;给…着色 
to change the colour of something using a chemical
  She stripped the floorboards and stained them dark brown. 她刮掉原来的漆,把地板刷成了深棕色。 
 - More examples
 - Water and other liquids can stain unprotected wood surfaces.
 - Lily pollen stains really badly.
 - Red wine stains.
 - The wood itself was light but I stained it darker.
 - You can stain wood in different colours.
 
  (SPOIL)      
C2 [ T ] literary败坏,玷污(名声等) 
to permanently spoil something such as someone's reputation
  Several important politicians have had their reputations stained by this scandal. 好几位重要的政界人士都因为这起丑闻而名声受损。 
 The country's history is stained with the blood of (= the country is guilty of killing) millions of innocent men and women. 这个国家的历史沾满了数百万无辜者的鲜血。 
 stain  
noun uk/steɪn/ us/steɪn/
  (MARK)        
 B1 [ C ]污渍;污点 
a dirty mark on something that is difficult to remove
  a blood/grass stain 血污/草渍 
 You can remove a red wine stain from a carpet by sprinkling salt over it. 地毯上红酒的污渍可以通过撒些盐来清除。 
  [ C ]染色剂;着色剂 
a chemical for changing the colour of something
   (DAMAGE)      
 [ S ] literary污点 
permanent damage to someone's reputation or character
  His solicitor said, "He leaves this court without a stain on his character." 他的律师说:“他走出法庭时名声将丝毫无损。”