Boost development of a fictional imp (13)
I believe the answer is:
amplification
'boost' is the definition.
(thesaurus)
'development of a fictional imp' is the wordplay.
'development of' is an anagram indicator (letters developed in another way).
'a'+'fictional'+'imp'='afictionalimp'
'afictionalimp' is an anagram of 'AMPLIFICATION'.
(Other definitions for amplification that I've seen before include "Means of making sound louder" , "Augmentation" , "Increasing of signals" .)