Pirates were often privateers, which fit that definition very well.
Furthermore, the overlap between piracy and warfare meant that many pirates served in paramilitary forces before, after, or during their pirate days. For an illustration, note this description of the Battle of New Orleans, including a prominent pirate acting as an irregular military advisor / commander, and many of his compatriots serving even in land-based artillery companies.
Pirates were often privateers, which fit that definition very well.
Furthermore, the overlap between piracy and warfare meant that many pirates served in paramilitary forces before, after, or during their pirate days. For an illustration, note this description of the Battle of New Orleans, including a prominent pirate acting as an irregular military advisor / commander, and many of his compatriots serving even in land-based artillery companies.