keep down

1.  Hold under control, repress; also, retain food. For example, Keep you voice down, or They vowed to keep down the insurgency, or With morning sickness, she had a hard time keeping down her breakfast. [Late 1500s]
2.  Prevent from increasing or succeeding, as in The government was determined to keep prices down, or Joyce felt that her lack of an advanced degree kept her down in terms of promotions. [Early 1800s]

The verb has 3 meanings:

Meaning #1: place a limit on the number of
  Synonym: number

Meaning #2: put down by force or intimidation
  Synonyms: repress, quash, subdue, subjugate, reduce

Meaning #3: manage not to throw up
  Antonym: vomit (meaning #1)