Yankee concern adopted by heavyweight industrialist (6)
I believe the answer is:
tycoon
'industrialist' is the definition.
(I have seen 'Powerful industrialist ' mean 'tycoon' so perhaps 'industrialist' could also mean 'tycoon')
'yankee concern adopted by heavyweight' is the wordplay.
'yankee' becomes 'Y' (phonetic alphabet: alpha, bravo, charlie etc.).
'concern' becomes 'co' (Abbreviation for company).
'adopted by' means one lot of letters goes inside another (I've seen this in other clues).
'heavyweight' becomes 'ton' (a ton weighs a lot).
'y'+'co'='yco'
'yco' inserted inside 'ton' is 'TYCOON'.
(Other definitions for tycoon that I've seen before include "Not coy? (anag)" , "Entrepreneur" , "Big noise" , "Magnate, wealthy businessman" , "Powerful industrialist" .)