CHAIR.

• chair
• 1 [countable] a piece of furniture for one person to sit on, which has a back, a seat, and four legs:
• a table and chairs
• in/on a chair
• He was sitting in a chair.
• He sank back into his chair.
• kitchen chair/garden chair etc
• 2 [singular] the position of being in charge of a meeting or committee, or the person who is in charge of it:
• Address your questions to the chair, please.
• be in the chair
• Who will be in the chair at tomorrow's meeting?
• chair of
• He was nominated as chair of the board of governors.
• 3 [countable] the position of being a university professor
• chair of
• a new Chair of Medicine
• 4

   the chair

  American English informal the electric chair
• Definition from the Longman Dictionary of Contemporary English 
• Advanced Learner's Dictionary.