Definitions of gag:

• noun:   restraint put into a person's mouth to prevent speaking or shouting
• noun:   a humorous anecdote or remark intended to provoke laughter

  Example: "He knows a million gags"

• verb:   prevent from speaking out

  Example: "The press was gagged"

• verb:   make an unsuccessful effort to vomit; strain to vomit
• verb:   cause to retch or choke
• verb:   struggle for breath; have insufficient oxygen intake

  Example: "He swallowed a fishbone and gagged"

• verb:   make jokes or quips

  Example: "The students were gagging during dinner"

• verb:   tie a gag around someone's mouth in order to silence them

  Example: "The burglars gagged the home owner and tied him to a chair"

• verb:   be too tight; rub or press