noun

• (military) A narrow excavation as used in warfare, as a cover for besieging or emplaced forces.
  "The soldiers in the trenches rely on logistical support."
• (archaeology) A pit, usually rectangular with smooth walls and floor, excavated during an archaeological investigation.
• (informal) A trench coat.
  "I was the first person in my high school to wear a trench and fedora constantly, and Ben was one of the first to wear a black trench."

verb

• (usually followed by upon) To invade, especially with regard to the rights or the exclusive authority of another; to encroach.
  "Shee is the Judge, Thou Executioner, Or if thou needs would'st trench upon her power, Thou mightst have yet enjoy'd thy crueltie, With some more thrift, and more varietie."
• (military, infantry) To excavate an elongated pit for protection of soldiers and or equipment, usually perpendicular to the line of sight toward the enemy.
  "No more shall trenching war channel her fields."
• (archaeology) To excavate an elongated and often narrow pit.