On the fast track.
en] To advance quickly towards a goal or destination.
On the fence.
On the fiddle.
On the firing line.
en] When one holds a position that it is likely to be criticized.
On the Fly.
On the fritz.
en] Not working correctly.
On the Home Stretch.
On the Internet nobody knows you're a dog.
On the lam.
On the level.
en] Honest, sincere, and straightforward.
On the line.
en] At risk.
On the Nose.
On the pig's back.
On the Q.T.
On the QT.
On the Radar.
On the record.
On the Right Track.
On the same page.
On the same wavelength.
en] Thinking in a similar way to someone.
On the shoulders of giants.
On the side of the angels.
On the Spot.
On the spur of the moment.
On the Take.
On the tip of your tongue.
en] When you are almost able to remember something, but you can't.
On the up and up.
On the wagon, off the wagon.
On the Wagon.
On the Warpath.
On thin ice.
On with the motley.
On your beam ends.
On your Tod.
On your toes.
en] Always be alert, ready to react, or ready for anything.
On your toes.
Onboard versus On Board.
en] Confusing Words
Once a man, twice a boy.
Once a man, twice a child.
Once a thief, always a thief.
Once a woman, twice a child.
Once an Eagle Scout, always an Eagle Scout.
Once an Eagle, always an Eagle.
Once bitten, twice shy.
Once in a blue moon.
Once in a While.
Once more unto the breach, dear friends, once more.
Once you go black, you never go back.
One (More) for the Road.
One and none is all one.
One Barber shaves not so close but another finds work.
One bitten by a snake for a snap dreads a rope for a decade.
One can run but one can't hide.
One cannot break a stick in a bundle.
One cannot break a twig in a bundle.
One cannot break sticks in a bundle.
One can't hold two watermelons in one hand.
One can't live with them, one can't live without them.
One eye of the masters sees more then ten of the servants.
One false move.
One fell swoop.
One flower makes no garland.
One fool makes an hundred.
One Foot in the Grave.
One for the Money, Two for the Show.
One for the Road.
One good turn deserves another.
One grain of sand can tip the scale.
One hair of a woman can draw more than a hundred pair of oxen.
One half of the world does not know how the other half lives.
One hand for oneself and one for the ship.
One hand washes the other.
One ill word asketh another.
One is not so soon healed as hurt.
One law for the rich and another for the poor.
One man's fish is another man's poison.
One man's junk is another man's treasure.
One man's meat is another man's poison.
One man's trash is another man's treasure.
One may as well hang for a sheep as a lamb.
One may sooner fall then rise.
One might as well be hanged for a sheep as a lamb.
One murder makes a villain, millions a hero.
One must become as humble as the dust before he can discover truth.
Mahatma Gandhi (1869 - 1948)
One nail drives out another.
fr] Un clou pousse l'autre.
One never looseth by doing good turns.
One over the eight.
One rotten apple will spoil the whole barrel.
One sandwich short of a picnic.
One scabbed sheep mars the whole flock.
One secret of happiness is being able to find joy in the joy of others.
Georges Bernanos (1888 - 1948)
One shrewd turn asks another.
One slumberr invites another.
One small step for man.
One stop shop.
One swallow does not a spring make.
One swallow does not a summer make.
One swallow does not make a spring.
One swallow does not make a summer.
One volunteer is worth ten pressed men.