one base hit
One boy is a boy, two boys half a boy, three boys no boy.
one by one
One can't make bricks without straw.
One cannot put back the clock.
One eyewitness is better than ten hearsays.
One false move may lose the game.
one foot in the grave
One generation plants the trees in whose shade another generation rests.
One good turn deserves another.
One hour today is worth two tomorrow.
one in hundred
One is never too old to learn.
One man's fault is other man's lesson.
One man's meat is another man's poison.
one month and a half
One never loses anything by politeness.
one night stand
one of a kind
one of several sides or parties
one's own profession
one's trump or master card
One's words reflect one's thinking.
one's year of birth considered in relation to the 12 Terrestrial Branches
one sided economy
one size fits all
One sows and another reaps.
one step ahead of you
One swallow does not make a summer.