Developed for use in a base (9)
I believe the answer is:
nefarious
'base' is the definition.
(thesaurus)
'developed for use in a' is the wordplay.
'developed' indicates an anagram.
'for'+'use'+'in'+'a'='foruseina'
'foruseina' anagrammed gives 'NEFARIOUS'.
(Other definitions for nefarious that I've seen before include "Very bad" , "immoral?" , "Villainous" , "Extremely wicked" , "Wicked, criminal" .)