The most common and most likely answer to this crossword clue is the 9 letter word EFFECTUAL
I've seen this crossword clue in The Daily Telegraph
E
F
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More clues leading to the result EFFECTUAL
Buddy explains!
The straight part
We know that "producing the intended result" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case producing the intended result = effectual.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.
What does EFFECTUAL mean?
EFFECTUAL adjective- Producing the intended result; entirely adequate.