The symbol # (4)
(Other definitions for hash that I've seen before include "Dish of diced meat etc - cannabis (slang)" , "reheated meat and vegetables" , "Meat dish; mess, jumble" , "chop into small pieces" , "Recycled food" .)
'the symbol' is the definition.
(ampersand is a kind of symbol)
This is all the clue.
(Other definitions for ampersand that I've seen before include "Symbol for 'and'" , "Pens drama using &" , "Man spared (anag.)" , "Union character" , "Plus sign" .)