[on a scratched horse] See: [PUT ONE'S MONEY ON A SCRATCHED […]

[on a shoestring] {adv. phr.} With little money to spend; on […]

[on a volcano] See: [SIT ON A VOLCANO].

[on account] {adv. phr.} As part payment of a debt; to […]

[on account of] {prep.} As a result of; because of. * […]

[on air] See: [WALK ON AIR].

[on all four] See: [HIT ON ALL FOUR].

[on all fours] {adv. phr.} 1. On all four legs; on […]

[on an average] or [on the average] {adv. phr.} In most […]

[on an even keel] {adv. phr.}, {informal} In a well-ordered way […]