Speaker

• speak‧er [countable]
• 1 someone who makes a formal speech to a group of people
• speaker at
• the guest speaker at the conference
• The keynote speaker (=main or most important speaker) was Robert Venturi, the architect.
• after-dinner speaker (=someone who makes a speech after a formal meal)
• 2 someone who speaks a particular language
• French-speaker/Spanish-speaker etc
• speaker of
• Some English words are difficult for speakers of other languages.
• a native speaker of Chinese
• 3 the part of a radio, sound system etc where the sound comes out
• 4 formal someone who says something:
• Pay attention to the body language of the speaker.
• 5

  the Speaker

   an official who controls discussions in a parliament
• 6

  the Speaker of the House

   the politician who controls discussions in the House of Representatives in the US Congress

Definition from the Longman Dictionary of Contemporary English
Advanced Learner's Dictionary.