The most common and most likely answer to this crossword clue is the 6 letter word CURDLE
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More clues leading to the result CURDLE
Buddy explains!
The straight part
We know that "Form a solid mass" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case form a solid mass = curdle.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 CURDLE mean?
CURDLE verb- To form curds so that it no longer flows smoothly; to cause to form such curds. (usually said of milk)
- To clot or coagulate; to cause to congeal, such as through cold. (metaphorically of blood)
- To cause a liquid to spoil and form clumps so that it no longer flows smoothly