less

less, lesser

这两个词都是little的比较级，都可指“较少”或“较小”。less偏重于“not so much”的意思，lesser偏重于“not so great或smaller、minor、lower”的意思。它们都可用于数量、重量、程度、重要性、价值等方面，但在用法及跟其他词语搭配上有很大不同，二者不能互换。
less: 所修饰的名词是不可数的，且没有冠词在前；less可带than，并指二者或多于二者的比较；

• i received less pay than he.
  我收的薪金比他少。
• i want less sugar for my coffee.
  我的咖啡要加少些糖。
• these days，i eat less rice than i used to.
  近来我吃饭比以前少。

lesser: 不用than，而用of，并只限于二者的比较；涉及程度、价值、重要性等方面时，一般用lesser（指 smaller，not so great，minor，lower）。

• i prefer a lesser amount of meat.
  我选择较少量的肉食。
• rice and wheat are two staple foods in china．in the north，rice is the lesser of the two.
  米和小麦是中国的两种主要食粮。在北方，米较小麦为次要。

形容词 less:

1. (comparative of `little' usually used with mass nouns) a quantifier meaning not as great in amount or degree
2. (usually preceded by `no') lower in quality
3. (nonstandard in some uses but often idiomatic with measure phrases) fewer

副词 less:

1. used to form the comparative of some adjectives and adverbs
   同义词：to a lesser extent
2. comparative of little

1. It rains less in London than in Manchester.
   伦敦的降雨量比曼彻斯特少。
2. He is less tall than she is.
   他不如她高。
3. Work more and dream less, you will be much happier.
   多做事少空想，这样你会愉快得多。