Single-masted sailboat (5)
I believe the answer is:
sloop
'single-masted sailboat' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sloop that I've seen before include "Single-masted sailing vessel" , "Sailing vessel with one mast" , "One-masted sailing boat" , "one going to sea" , "Single-masted sailing boat" .)