The most common and most likely answer to this crossword clue is the 9 letter word REFORMERS
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Buddy explains!
The straight part
We know that "Progressives" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case progressives = reformers.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 REFORMERS mean?
REFORMERS noun- One who reforms, or who works for reform.
- (history) One who was involved in the Reformation.
- (chemical engineering, fuel cells) A device which converts hydrocarbons into a hydrogen-rich mixture of gases.
- (chemical engineering) A device used to convert petroleum refinery naphthas, typically having low octane ratings, into high-octane liquid products called reformates.