An Arab boat? Very much so! (3,3)
I believe the answer is:
and how
'so' is the definition.
Both the answer and definition are adverbs. Perhaps there's a link between them I don't understand?
'an arab boat? very much' is the wordplay.
'arab boat?' becomes 'dhow' (I've seen this before).
'very' becomes 'v' (common abbreviation).
'much' means to remove the last letter (much but not all of the word).
'an'+'dhow'+'v'='andhowv'
'andhowv' with its final letter taken away is 'AND HOW!'.
(Another definition for and how that I've seen is " Certainly".)