Slips water rat among cages (6)
I believe the answer is:
errata
'slips' is the definition.
(slip can mean an error or mistake)
'water rat among cages' is the wordplay.
'cages' indicates a hidden word (the answer is caged or held).
'ERRATA' is hidden within 'water rat among'.
(Other definitions for errata that I've seen before include "Mistakes (Latin)" , "Mistakes in printed proofs" , "mistakes in print" , "List of errors" , "corrected mistakes" .)