Definition of "on all fours"

on all fours

adverb
not comparable
1. (idiomatic) On one's hands and knees.
  Quotations
  A bulky form was seen rising aft, and began marching on all fours with the movements of some big cautious beast.
  1897, Joseph Conrad, chapter 3, in The Nigger Of The ‘Narcissus’
  He was on all fours, with three children on his back, riding him for a horse.
  1916, Elbert Hubbard, “Johannes Brahms”, in Little Journeys Vol. 14: Great Musicians
2. (idiomatic, often followed by "with") In a manner which is similar in nature or effect to something else; consistently.
  Quotations
  The paternal longing ran on all fours with her own desire.
  1886 May – 1887 April, Thomas Hardy, chapter 39, in The Woodlanders […], volumes (please specify |volume=I to III), London, New York, N.Y.: Macmillan and Co., published 1887
  The new law was precisely on all-fours with the Homestead Act.
  1920, Rudyard Kipling, chapter 21, in Letters of Travel