Definify.com
Webster 1913 Edition
All fours
Allˊ fours′
[formerly,
All` four"
.] All four legs of a quadruped; or the two legs and two arms of a person.
To be
, go
, or run
,
on all fours
to be on the same footing; to correspond (with) exactly; to be alike in all the circumstances to be considered.
“This example is on all fours with the other.” “No simile can go on all fours.” Macaulay.