Deposit is returned to lieutenant (4)
I believe the answer is:
silt
'deposit' is the definition.
(thesaurus)
'is returned to lieutenant' is the wordplay.
'returned' is a reversal indicator.
'to lieutenant' becomes 'lt'.
'is' back-to-front is 'si'.
'si'+'lt'='SILT'
(Other definitions for silt that I've seen before include "Muddy deposit" , "Slimy mud" , "Fine river sediment" , "Fine deposited material" , "Fine sediment (often deposited by water)" .)