speak vs voice

speak

verb
  • To produce a sound; to sound. 

  • To communicate with one's voice, to say words out loud. 

  • To understand (as though it were a language). 

  • To have a conversation. 

  • To utter. 

  • To be able to communicate in a language. 

  • Of a bird, to be able to vocally reproduce words or phrases from a human language. 

  • To deliver a message to a group; to deliver a speech. 

  • To be able to communicate in the manner of specialists in a field. 

  • To communicate or converse by some means other than orally, such as writing or facial expressions. 

  • To communicate (some fact or feeling); to bespeak, to indicate. 

noun
  • Speech, conversation. 

  • language, jargon, or terminology used uniquely in a particular environment or group. 

voice

verb
  • To fit for producing the proper sounds; to regulate the tone of 

  • To assign the voice flag to a user on IRC, permitting them to send messages to the channel. 

  • To act as a voice actor to portray a character. 

  • To give utterance or expression to; to utter; to publish; to announce 

  • To utter audibly, with tone and not just breath. 

noun
  • Sound uttered by the mouth, especially by human beings in speech or song; sound thus uttered considered as possessing some special quality or character 

  • The tone or sound emitted by an object 

  • That which is communicated; message; meaning. 

  • Sound made through vibration of the vocal cords; sonant, or intonated, utterance; tone; — distinguished from mere breath sound as heard in whispering and voiceless consonants. 

  • An expressed opinion, choice, will, desire, or wish; the right or ability to make such expression or to have it considered 

  • A particular style or way of writing that expresses a certain tone or feeling. 

  • A particular way of inflecting or conjugating verbs, or a particular form of a verb, by means of which is indicated the relation of the subject of the verb to the action which the verb expresses. 

  • In harmony, an independent vocal or instrumental part in a piece of composition. 

  • A flag associated with a user on a channel, determining whether or not they can send messages to the channel. 

  • One who speaks; a speaker. 

  • The faculty or power of utterance 

How often have the words speak and voice occurred in a corpus of books? (source: Google Ngram Viewer )