The Collaborative International Dictionary of English v.0.48:

Speaker \Speak"er\, n.
   1. One who speaks. Specifically:
      (a) One who utters or pronounces a discourse; usually, one
          who utters a speech in public; as, the man is a good
          speaker, or a bad speaker.
      (b) One who is the mouthpiece of others; especially, one
          who presides over, or speaks for, a delibrative
          assembly, preserving order and regulating the debates;
          as, the Speaker of the House of Commons, originally,
          the mouthpiece of the House to address the king; the
          Speaker of a House of Representatives.
          [1913 Webster]

   2. A book of selections for declamation. [U. S.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

speaker
    n 1: someone who expresses in language; someone who talks
         (especially someone who delivers a public speech or someone
         especially garrulous); "the speaker at commencement"; "an
         utterer of useful maxims" [syn: speaker, talker,
         utterer, verbalizer, verbaliser]
    2: electro-acoustic transducer that converts electrical signals
       into sounds loud enough to be heard at a distance [syn:
       loudspeaker, speaker, speaker unit, loudspeaker
       system, speaker system]
    3: the presiding officer of a deliberative assembly; "the leader
       of the majority party is the Speaker of the House of
       Representatives"

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "speaker":
   acoustical network, capacitor speaker, chair, chairman, chatterbox,
   coaxial speaker, cone, convener, conversationalist,
   crossover network, debater, declaimer, demagogue, diaphragm,
   dynamic speaker, earphone, electrodynamic speaker,
   electromagnetic speaker, electrostatic speaker,
   excited-field speaker, full-fidelity speaker, haranguer, headphone,
   headset, herald, high-fidelity speaker, high-frequency speaker,
   horn, jawsmith, keynoter, lecturer, loudspeaker,
   low-frequency speaker, midrange speaker, monorange speaker, mouth,
   mouthpiece, moving-coil speaker, official spokesman, orator,
   panelist, patterer, permanent magnet speaker, presiding officer,
   prolocutor, prolocutress, prolocutrix, public speaker,
   rabble-rouser, ranter, rapporteur, reporter, sayer, speaker system,
   speaker unit, speecher, speechifier, speechmaker, spieler,
   spokesman, spokesperson, spokeswoman, spouter, talker,
   triaxial speaker, tub-thumper, tweeter, utterer, voice, voice coil,
   woofer



The Free On-line Dictionary of Computing (30 December 2018):

speaker

   1.  loudspeaker.

   2. The person who is (assumed to be) talking.

   (1996-12-01)