Boat behind base (6)
I believe the answer is:
bottom
I believe this is a triple definition!
'boat' is the first definition.
(thesaurus)
'behind' is the second definition.
(synonyms)
'base' is the third definition.
(I've seen this before)
(Other definitions for bottom that I've seen before include "mechanic, for instance" , "Shakespearean - rear" , "Shakespeare's weaver" , "Quark's flavour" , "Crack" .)