The most common and most likely answer to this crossword clue is the 5 letter word CLUNK
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The straight part
We know that "‘dumbo" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ‘dumbo = clunk.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 CLUNK mean?
CLUNK noun- A dull, metallic sound, especially one made by two bodies coming into contact.
- The sound of liquid coming out of a bottle, etc.; a glucking sound.
- To make such a sound