The most common and most likely answer to this crossword clue is the 4 plus 3 letter word CASH COW
I've seen this crossword clue in The Guardian
C
A
S
H
C
O
W
More clues leading to the result CASH COW
- Caught a musical, say, about Charlie, a real money earner
- Profitable business needing lower maintenance?
- Timber business in outskirts of Chepstow, money spinner
- Brief example: how to invest capital in company that makes money
- Good earner’s to brag after market slump — that’s never right
- Get ready for lower profits from this easy business?
- Bully for Johnny’s nice little earner
- Successful investment in the stock market?
- Wimbledon champ, bully, gets easy money
- Remains with company in outskirts of Cracow, a money-spinner
Buddy explains!
The straight part
We know that "established income earner" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case established income earner = cash cow.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.