whoa vs wo

whoa

intj
  • Stop (especially when commanding a horse or imitative thereof); calm down; slow down. 

  • An expression of surprise. 

  • Used as a meaningless filler in song lyrics. 

verb
  • To attempt to slow (an animal) by crying "whoa". 

wo

intj
  • A call to cause a horse to slow down or stop; whoa. 

  • A falconer's call to a hawk. 

noun
  • A wall. 

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