Prow of sailing boat in outline (6)
I believe the answer is:
sketch
'outline' is the definition.
(I know that outline can be written as sketch)
'prow of sailing boat' is the wordplay.
'prow of' suggests taking the first letters (prow means the front of a boat).
'boat' becomes 'ketch' (ketch is a type of sailing boat).
The initial letter of 'sailing' is 's'.
's'+'ketch'='SKETCH'
'in' acts as a link.
(Other definitions for sketch that I've seen before include "Unfinished drawing" , "Outline - preliminary drawing" , "Short comic routine" , "Short humorous scene" , "draft" .)