Vail means to lower as a sign of respect.
- You should vail the flag because our former governor just died.
Vale refers to a valley.
- His walk took him through vale country and agricultural land.
Veil is a face covering or something that conceals or obscures.
- The women wear a black veil to hide their faces.
- Their organization operated under a veil of secrecy.
- They have always veiled their undercover activities.