Difficult to carry one off — primarily this style (6)
I believe the answer is:
hairdo
'this style' is the definition.
(I've seen this before)
'difficult to carry one off primarily' is the wordplay.
'difficult' becomes 'hard' (associated in meaning).
'to carry' indicates putting letters inside.
'one' becomes 'I' (Roman numeral).
'primarily' indicates taking the first letters.
The first letter of 'off' is 'o'.
'hard' going around 'i' is 'haird'.
'haird'+'o'='HAIRDO'
(Other definitions for hairdo that I've seen before include "Bob, for one" , "What one may have expected from 'Sweeney Todd'" , "Say, crew cut" , "Cut and set" , "Bob, perm or bouffant" .)