Attempt to include a salver (4)
I believe the answer is:
tray
'salver' is the definition.
(I've seen this before)
'attempt to include a' is the wordplay.
'attempt to' becomes 'try' (I can't explain this - if you can you should give a lot more credence to this answer).
'include' indicates putting letters inside.
'try' enclosing 'a' is 'TRAY'.
Can you help me to learn more?
(Other definitions for tray that I've seen before include "Flat utensil for carrying food" , "Informal meal" , "Flat plate for carrying things" , "Shallow receptable for carrying something" , "Flat carrier" .)