The most common and most likely answer to this crossword clue is the 5 letter word LEFTY
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More clues leading to the result LEFTY
Buddy explains!

The straight part
We know that "Socialist" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case socialist = lefty.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 LEFTY mean?
LEFTY noun- One who is left-handed.
- One who has left-wing political views.
- One's left testicle.
- Left-handed.
- Intended for left-handed use.
- Left-wing.