The most common and most likely answer to this crossword clue is the 7 letter word JUBILEE
J
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More clues leading to the result JUBILEE
- Anniversary could be Julie’s undoing
- Festival month sees indefinite number succumbing to ill temper
- Great rejoicing when Jack meets topless sexy Oriental!
- First of all join us British in loyal expressive exuberance during this time of celebration
- June, Bill, and Leah partly ushering in English party
- Line of underground humour not new in summer month
Buddy explains!

The straight part
We know that "Line of underground" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case line of underground = jubilee.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 JUBILEE mean?
JUBILEE noun- (Jewish history) A special year of emancipation supposed to be kept every fifty years, when farming was abandoned and Hebrew slaves were set free.
- A 25th, 40th, 50th, 60th or 70th anniversary.
- A special year (originally held every hundred years, then fifty, and then fewer) in which remission from sin could be granted as well as indulgences upon making a pilgrimage to Rome.
- A time of celebration or rejoicing.
- An occasion of mass manumission from slavery.
- A period of fifty years; a half-century.