Flipping short time filling certain form (9)
I believe the answer is:
structure
'form' is the definition.
(thesaurus)
'flipping short time filling certain' is the wordplay.
'flipping' says the letters should be written in reverse.
'short' becomes 'curt' (synonyms).
'time' becomes 't' (abbreviation).
'filling' means one lot of letters goes inside another.
'certain' becomes 'sure' (synonyms).
'curt' reversed gives 'truc'.
'truc'+'t'='truct'
'truct' put into 'sure' is 'STRUCTURE'.
(Other definitions for structure that I've seen before include "Building or organised arrangement" , "Building; framework" , "Edifice" , "make-up" .)