Urinated on the counter, which is meaningful (4)
I believe the answer is:
deep
'is meaningful' is the definition.
(I've seen this in another clue)
'urinated on the counter' is the wordplay.
'urinated' becomes 'peed' ('pee' can be a synonym of 'urinate').
'on the counter' is a reversal indicator (counter can mean in the opposite direction).
'peed' reversed gives 'DEEP'.
'which' is the link.
(Other definitions for deep that I've seen before include "Main" , "late" , "Sunk low" , "Extending far down" , "Intense; low (in pitch)" .)