The most common and most likely answer to this crossword clue is the 7 letter word SIXTIES
I've seen this crossword clue in The Guardian
S
I
X
T
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E
S
Buddy explains!
The straight part
We know that "decade" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case decade = sixties.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 SIXTIES mean?
SIXTIES noun- The decade of the 1860s, 1960s, etc. (but especially the 1960s)
- A period in American history centered around the counterculture movement of the late 1960s.
- The decade of one's life from age 60 through age 69.
- (temperature, rates) The range between 60 and 69.
- From or evoking the 61st through 70th years of a century (chiefly the 1960s).