There are many synonyms for the term "fire to pin down someone." One of the most common synonyms is "grill," which refers to questioning someone in an intense and persistent manner in order to get information from them. Another synonym is "interrogate," which implies a more formal or official manner of questioning, often in a legal or law enforcement setting. Other synonyms include "cross-examine," "examine," "probe," and "pump." All of these terms suggest a focused and determined effort to elicit information from someone who may be unwilling or reluctant to reveal it. Whether in a legal or personal context, the use of these synonyms requires a skillful and strategic approach in order to successfully pin down the person in question.