Outline of small two-master (6)
I believe the answer is:
sketch
'outline' is the definition.
(synonyms)
'small two-master' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'two-master' becomes 'ketch' (I've seen this before).
's'+'ketch'='SKETCH'
'of' is the link.
(Other definitions for sketch that I've seen before include "draft" , "Short humorous scene" , "Short comic routine" , "Dead parrot featured in one" , "Portrait" .)