Extent downwards (5)
I believe the answer is:
depth
(Other definitions for depth that I've seen before include "sometimes leading to charge for sailors at war?" , "Insight" , "Measurement from front to back" , "Profoundness" , "Deepness" .)
I believe the answer is:
depth
(Other definitions for depth that I've seen before include "sometimes leading to charge for sailors at war?" , "Insight" , "Measurement from front to back" , "Profoundness" , "Deepness" .)