Initially discovered the way to build a boat (4)
I believe the answer is:
'a boat' is the definition.
(dhow is a kind of sailing vessel)
'initially discovered the way' is the wordplay.
'initially' suggests taking the first letters.
'the way' becomes 'how' (I've seen this in another clue).
The first letter of 'discovered' is 'd'.
'to build' is the link.
(Other definitions for dhow that I've seen before include "Type of boat used in the Indian ocean" , "Arab sailer" , "Arab sailing boat" , "Arab coastal vessel" , "Arab vessel with lateen sail" .)