Definition of "nighthawk"

(UK, regional) A nightjar, especially Caprimulgus europaeus (Eurasian nightjar).  examples

(US) A New World nightjar of the genus Chordeiles, especially Chordeiles minor.  quotations  examples

A person whose preference or custom is to remain awake and active during the night and the early morning hours.  examples

A nighthawker (metal detectorist who works illegally at night).  examples