ALL-FOURS, noun [all and four.] A game at cards, played by two or four persons; so called from the possession of the four honors, by one person, who is then said to have all fours. To go on all fours is to move or walk on four legs, or on the two legs and two arms.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI