Elizabeth includes us in commercial enterprise (8)
I believe the answer is:
business
'commercial enterprise' is the definition.
(synonyms)
'elizabeth includes us in' is the wordplay.
'elizabeth' becomes 'Bess' (nickname).
'includes' means one lot of letters goes inside another.
'us'+'in'='usin'
'bess' placed around 'usin' is 'BUSINESS'.
(Other definitions for business that I've seen before include "Affair - matters to be attended to" , "Profession - trade - matter" , "Commerce, trace" , "Work - shop" , "Commercial or industrial enterprise" .)