The most common and most likely answer to this crossword clue is the 7 letter word FIFTIES
I've seen this crossword clue in The Guardian
F
I
F
T
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S
Buddy explains!

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 FIFTIES mean?
FIFTIES noun- The decade of the 1850s, 1950s, etc.
- The decade of one's life from age 50 through age 59.
- (temperature, rates) The range between 50 and 59.
- From or evoking the 51st through 60th years of a century (chiefly the 1950s).
- A banknote or coin with a denomination of 50.
- A batsman's score of at least 50 runs and less than 100 runs.