underdrain

under- +‎ drain

underdrain (plural underdrains)

1. An underground drain or trench with openings through which the water may percolate from the soil or ground above.

underdrain (third-person singular simple present underdrains, present participle underdraining, simple past and past participle underdrained)

1. (transitive) To drain by forming an underdrain or underdrains in.

• underdrainage

• did a runner