Guard rank surrounding lieutenant (7)
I believe the answer is:
shelter
'guard' is the definition.
(thesaurus)
'rank surrounding lieutenant' is the wordplay.
'rank' becomes 'sheer' ('sheer' can be a synonym of 'rank'**).
'surrounding' is an insertion indicator.
'lieutenant' becomes 'lt'.
'sheer' going around 'lt' is 'SHELTER'.
(Other definitions for shelter that I've seen before include "Refuge, protection" , "Refuge or protective cover" , "Housing or haven" , "Give protection" , "Let hers go into shielded place" .)