Being definite groups, they're worth having (6)
I believe the answer is:
assets
'worth having' is the definition.
I can't tell whether this defines the answer.
'being definite groups' is the wordplay.
'being definite' becomes 'as' (I can't justify this - if you can you should believe this answer much more).
'groups' becomes 'sets' (a set is a group of things).
'as'+'sets'='ASSETS'
'they're' acts as a link.
Can you help me to learn more?
(Other definitions for assets that I've seen before include "valued possessions" , "Possessions and resources" , "Valuable resources" , "One's goods and property" , "Property owned by person or business" .)
