There's profundity in what a plumber may find (5)

I believe the answer is:

depth

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But I can't explain it at all! Could you help me understand?

(Other definitions for depth that I've seen before include "Profoundness" , "sometimes leading to charge for sailors at war?" , "Measurement from front to back" , "Distance from top down as in water" , "Military life; vulgarly artificial" .)

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