Work with uncle, struggling to gain energy to make wealth (8)
I believe the answer is:
opulence
'wealth' is the definition.
(opulence is a kind of wealth)
'work with uncle struggling to gain energy' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'with' is a charade indicator (letters next to each other).
'struggling' indicates anagramming the letters.
'to gain' means one lot of letters goes inside another.
'energy' becomes 'e' (physics symbol as in E=mcp).
'uncle' anagrammed gives 'ulnce'.
'ulnce' enclosing 'e' is 'ulence'.
'op'+'ulence'='OPULENCE'
'to make' acts as a link.
(Other definitions for opulence that I've seen before include "Profusion, luxury" , "wealth is manifest" , "Ostentatious luxury" , "Conspicuous wealth" , "Fortune" .)