Dictionary includes “beer” as local usage (7)
I believe the answer is:
dialect
'local usage' is the definition.
(language used in a particular area)
'dictionary includes beer' is the wordplay.
'dictionary' becomes 'dict'.
'includes' indicates putting letters inside.
'beer' becomes 'ale' (type of beer).
'dict' placed around 'ale' is 'DIALECT'.
'as' is the link.
(Other definitions for dialect that I've seen before include "talk from the regions" , "Local form of language" , "Manner of speaking" , "Talk of the district" , "Local lingo" .)