Jack and Simon, say, wearing something waterproof (9)
I believe the answer is:
tarpaulin
'something waterproof' is the definition.
I know that 'waterproof' relates to this answer.
'jack and simon say wearing' is the wordplay.
'jack' becomes 'tar' (both are informal terms for sailor).
'and' says to put letters next to each other.
'simon say' becomes 'paul' (I can't explain this - if you can you should give a lot more credence to this answer).
'wearing' becomes 'in' (in certain clothing).
'tar'+'paul'+'in'='TARPAULIN'
Can you help me to learn more?
(Other definitions for tarpaulin that I've seen before include "Waterproof canvas used as covering" , "It provides protection" , "Waterproof cloth" , "Heavy waterproof cover" , "[SHHET]" .)