The most common and most likely answer to this crossword clue is the 11 letter word OUT-OF-DATE
I've seen this crossword clue in Independent
O
U
T
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O
F
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D
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More clues leading to the result OUT-OF-DATE
Buddy explains!
The straight part
We know that "no longer valid?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case no longer valid? = out-of-date.The cryptic/wordplay part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What does OUT-OF-DATE mean?
OUT-OF-DATE adjective- Alternative form of out of date