Author is writer of particular kind of verse (6)
I believe the answer is:
iambic
'of particular kind of verse' is the definition.
(iambic verse is a type of poetry)
'author is writer' is the wordplay.
'author is' becomes 'I am' (referring to the author of the crossword).
'writer' becomes 'bic' (kind of pen).
'iam'+'bic'='IAMBIC'
(Other definitions for iambic that I've seen before include "Type of verse" , "Poetic metre with unstressed-stressed syllables" , "Kind of metric foot in poetry" , "Using short-long metrical feet" , "Kind of verse form with lines of five feet, each with two syllables" .)