Grab mischievous child on ship (7)
I believe the answer is:
impress
'grab' is the definition.
(thesaurus)
'mischievous child on ship' is the wordplay.
'mischievous child' becomes 'imp' (I've seen this before).
'on' becomes 're' ('on' can be mean 'with reference to').
'ship' becomes 'ss'.
'imp'+'re'+'ss'='IMPRESS'
(Other definitions for impress that I've seen before include "Simpers to affect favourably" , "strike" , "Influence - conscript - stamp" , "Mark made by a seal or stamp" , "Fix deeply in the mind" .)