big business 
noun [mass noun]
Large-scale or important financial or commercial activity: the children’s toy market is big business now...
- They are ineptly led and cut off from important sections of big business by their line over Europe.
- They say the summit's aims of free trade and open borders help big business and hurt the poor.
- What the American experience tells us is that farmers' markets are big business.
- ondinging
- on-disc
- on-disk
- on dit
- ondol
- on draught
- on drive
- on drugs
- one
- -one
- one-act
- one-acter
- one after another (or the other)
- O'Neal, Shaquille
- one (also a) (great) big happy family
- one and all
- one and only
- one and the same
- one another
- one-argument
- one-arm
- one-arm bandit
- one-armed
- one-armed bandit
- one-armed paper-hanger