Hesitation about pretty covering is necessary (9)
I believe the answer is:
requisite
'necessary' is the definition.
(I've seen this before)
'hesitation about pretty covering is' is the wordplay.
'hesitation' becomes 'er'.
'about' says the letters should be written in reverse.
'pretty' becomes 'quite' ('quite' can be a synonym of 'pretty'**).
'covering' is an insertion indicator.
'er' written backwards gives 're'.
'quite' enclosing 'is' is 'quisite'.
're'+'quisite'='REQUISITE'
(Other definitions for requisite that I've seen before include "Necessary" , "Indispensable" , "Totally essential" , "Needful" .)