The most common and most likely answer to this crossword clue is the 5 plus 3 letter word POLKA DOT
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Buddy explains!
The straight part
We know that "popular dress design" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case popular dress design = polka dot.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 POLKA DOT mean?
POLKA DOT noun- Any of a number of uniform round dots, repeated to make a regular geometric pattern on a fabric