Characteristic style of Oscar Wilde I am occasionally to cover (5)
I believe the answer is:
idiom
'characteristic style' is the definition.
(I've seen this before)
'oscar wilde i am occasionally to cover' is the wordplay.
'oscar' becomes 'O' (phonetic alphabet: alpha, bravo, charlie etc.).
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
'to cover' indicates putting letters inside.
'wilde'+'i'+'am'='wildeiam'
The alternate letters of 'wildeiam' are 'idim'.
'o' put into 'idim' is 'IDIOM'.
'of' is the link.
(Other definitions for idiom that I've seen before include "Colloquial saying" , "Figure of speech" , "Characteristic style, vocabulary" , "Local style of expression" , "Artistic style" .)