an exact definition; 确切的定义
To give a definition of a word is more difficult than to give an illustration of its use. 给一个词下定义要比举例说明它的用法困难。
be defined as ... 被定义为 ...
牛津高阶第八版
美国韦氏词典
Dictionary.com
Free Dictionary
维基百科 (自由的百科全书)