Also found in: Dictionary.
1. To force a liquid or gas into someone or something through the use of a pump. A noun or pronoun can be used between "pump" and "in." They've been pumping oxygen in, but the patient still hasn't responded. You need to use the primer on the lawn mower to pump in enough gasoline for the carburetor to work properly.
2. To provide large amounts of money to something, such as a company, project, or business venture. A noun or pronoun can be used between "pump" and "in." The billionaire has been pumping in millions of his own dollars to fund the new space exploration mission. I'm afraid it's time to cut our losses and close the store—we've pumped too much money in as it is.
See also: pump