The most common and most likely answer to this crossword clue is the 8 letter word ASSONANT
I've seen this crossword clue in The Daily Telegraph
A
S
S
O
N
A
N
T
More clues leading to the result ASSONANT
- Similar-sounding old name given to animal and insect
- Kind of rhyming, as “kid set on insect”
- Harmonious like child with a set of books
- Buffoon in contact with six-footer having correspondence
- Corresponding in sound from donkey close to insect
- Using vocal harmony in unwise arrangement for Bremen-style musicians?
Buddy explains!
The straight part
We know that "Harmonious" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case harmonious = assonant.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.