Here are the possible solutions for trench filled to ground level clue
Answer
Clue
Relevancy
frenchdrain
Clue
Trench filled to ground level
moat
Clue
Water-filled trench
Water-filled trench surrounding a castle
Definition
to surround with a water-filled trench
ozone
Clue
Low-level pollution or high-level protection
Definition
an allotropic form of oxygen present in the atmosphere
ptomaineconcourse
Clue
Warning sign at a train station's food court? (NOTE: The original sign, without my additions, actually exists. It's in Grand Central Terminal in NYC, on the lower level — the food court level. The sig
