noun

• (historical, law, properly, rare) A privilege of some feudal lords permitting them to execute summary judgment upon thieves (particularly their own tenants) captured outside their estates and to keep any chattels forfeited upon conviction.
  "A grant of outfangthief imports the trial of those of his fee taken for felony in another precinct."
• (historical, law, generally, rare) A privilege of some feudal lords permitting them to execute summary judgment upon all thieves captured within their estates, regardless of their origin.
  "But feudalism also contained another principle, and that was, that within his own territory each lord was absolute; his suzerain could not interfere with his jurisdiction; infangthief and outfangthief implied a very perfect and intelligible power of hanging and imprisoning as he pleased."
• (historical, law, rare, countable) A thief so captured and tried.