An interrogator is the person who does the hard questioning — the one who sits across from you and keeps asking, often for a long time, to get information. In police, military, and spy stories this is a job, sometimes feared. The word names the doer, not the act and not the questions themselves. Though actually, the same spelling is also a machine: in electronics an interrogator is a device that sends a signal and reads the reply, as with some ID tags. That technical sense is real, but the human meaning is the one learners meet first. It is a formal, rather cold noun; in ordinary talk people more often say the officer, or the person who questioned him.