Inspiration’s essentially difficult with deviated septum (7)
I believe the answer is:
impetus
'inspiration's' is the definition.
(thesaurus)
'essentially difficult with deviated septum' is the wordplay.
'essentially' indicates the central letters.
'with' is a charade indicator (letters next to each other).
'deviated' is an anagram indicator (I've seen 'deviating' mean this).
The central letter of 'difficult' is 'i'.
'septum' is an anagram of 'mpetus'.
'i'+'mpetus'='IMPETUS'
(Other definitions for impetus that I've seen before include "Momentum, stimulus" , "Driving force, forward movement" , "Force that moves something along" , "Incentive, stimulus" , "Drive" .)