The most common and most likely answer to this crossword clue is the 12 letter word UNSATISFYING
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More clues leading to the result UNSATISFYING
Buddy explains!
The straight part
We know that "Lacking content: fully sustaining? That’s wrong!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lacking content: fully sustaining? that’s wrong! = unsatisfying.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.
Crossword Answer definitions
UNSATISFYING adjective- Not providing satisfaction.