speaker  
noun [ C ] uk/ˈspiː.kər/ us/ˈspiː.kɚ/
  (FORMAL TALK)      
 B1 发言者;演讲者
a person who gives a speech at a public event
  a good public speaker 擅长公开演讲的人 
 Please join with me in thanking our guest speaker tonight. 请大家和我一起向今晚的特邀演讲人表示感谢。 
 The Democrats have chosen the Texas state treasurer as the keynote (= most important) speaker at their convention. 民主党人选择了得克萨斯州财政部长作为他们大会上的主要发言人。 
 - More examples
 - In his opening salvo the speaker fiercely attacked the government's record on healthcare.
 - She is a confident and self-possessed public speaker.
 - The speaker sidestepped the question by saying that it would take him too long to answer it.
 - The speaker was applauded as he tore apart the prime minister's policies.
 - A huge throng had gathered round the speaker.
 
  (LANGUAGE)      
 B1 (说某一特定语言的)说话者;演讲人
someone who speaks a particular language
  a French speaker 说法语的人 
 a fluent Russian speaker 说一口流利的俄语的人 
 non-English speakers 不是说英语的人 
   (ELECTRICAL)      
A2 扬声器,喇叭
the part of a radio, television, or computer, or of a piece of electrical equipment for playing recorded sound, through which the sound is played. A speaker can be part of the radio, etc. or be separate from it
  There's no sound coming out of the right-hand speaker. 右边的喇叭不出声了。