The most common and most likely answer to this crossword clue is the 6 letter word SCREED
I've seen this crossword clue in Independent
S
C
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D
More clues leading to the result SCREED
- Mortar used for levelling a long passage
- Long speech made by saint on faith
- It smoothly finishes off a long passage
- Long speech where credit is in issue
- Singular statement of beliefs in long document
- Belief under leadership of Salmond in diatribe
- Belief follows opening of scriptural passage
- Long dull passage covered in loose rock, apparently
- Daughter by cliff-face rocks writing
- Strip on bedroom floor? Spouse initially needed persuasion
Buddy explains!

The straight part
We know that "long document" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case long document = screed.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 SCREED mean?
SCREED noun- A piece or narrow strip cut or torn off from a larger whole; a shred.
- A piece of land, especially one that is narrow.
- A rent, a tear.
- A piece of writing (such as an article, letter, or list) or a speech, especially if long.
- (by extension) A speech or piece of writing which contains angry and extended criticism; a diatribe, a harangue.
- Chiefly in the plural form screeds: a large quantity.
- Senses relating to building construction and masonry.
- To rend, to shred, to tear.
- To read or repeat from memory fluently or glibly; to reel off.
- To use a screed to produce a smooth, flat surface of concrete, plaster, or similar material; also (generally) to put down a layer of concrete, plaster, etc.
- To become rent or torn.
- A (discordant) sound or tune played on bagpipes, a fiddle, or a pipe.
- The sound of something scratching or tearing.
- To play bagpipes, a fiddle, or a pipe.
- To make a discordant or harsh scratching or tearing sound.
- To play (a sound or tune) on bagpipes, a fiddle, or a pipe.
- Strewn with scree.