Incomplete sauce boat (5)
I believe the answer is:
ketch
This clue might be a double definition.
'incomplete sauce' is the first definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'boat' is the second definition.
(ketch is a kind of sailing vessel)
Can you help me to learn more?
(Other definitions for ketch that I've seen before include "Two-masted sailing vessel" , "Two-masted sailing ship" , "Jack" , "Two-masted sailing boat" , "Small sailing vessel with two masts" .)