The most common and most likely answer to this crossword clue is the 7 letter word DANDIES
I've seen this crossword clue in The Guardian
D
A
N
D
I
E
S
More clues leading to the result DANDIES
Buddy explains!
The straight part
We know that "swells" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case swells = dandies.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 DANDIES mean?
DANDIES noun- A man very concerned about his clothes and his appearance.
- A yawl, or a small after-sail on a yawl.
- A dandy roller.