A certain arrangement of sail in fashion that's novel (8,6)
I believe the answer is:
treasure island
'novel' is the definition.
(I've seen this before)
'a certain arrangement of sail in fashion' is the wordplay.
'certain' becomes 'sure' ('sure' can be a synonym of 'certain').
'arrangement of' is an anagram indicator.
'in' indicates putting letters inside.
'fashion' becomes 'trend' (I've seen this before**).
'sail' is an anagram of 'isla'.
'a'+'sure'+'isla'='asureisla'
'asureisla' placed into 'trend' is 'TREASURE ISLAND'.
'that's' is the link.
(Other definitions for treasure island that I've seen before include "Book by Stevenson" , "Classic adventure story" , "R.L. Stevenson novel" , "Long John Silver tale" , "Tale of adventure" .)