Definition of "nighthawk"

nighthawk

/ˈnʌɪthɔːk/

noun
plural nighthawks
1. (UK, regional) A nightjar, especially Caprimulgus europaeus (Eurasian nightjar).
2. (US) A New World nightjar of the genus Chordeiles, especially Chordeiles minor.
  Quotations
  The swallows circled around and I watched them and the night-hawks flying above the roofs and drank the Cinzano.
  1929, Ernest Hemingway, A Farewell to Arms, Folio Society, published 2008, page 91
3. A person whose preference or custom is to remain awake and active during the night and the early morning hours.
4. A nighthawker (metal detectorist who works illegally at night).