Meaning of underdrain

un•der•drain

Pronunciation: (n.un'dur-drān"v.un"dur-drān'), [key]
— n.
  1. a drain placed beneath the surface of cultivated fields, streets, etc.
—v.t.
  1. to equip or supply with an underdrain or underdrains.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.