The most common and most likely answer to this crossword clue is the 11 letter word COPPERPLATE
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The straight part
We know that "Handwriting" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case handwriting = copperplate.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 COPPERPLATE mean?
COPPERPLATE noun- A copper plate, either etched or engraved, to make a recessed pattern.
- A print made from such a plate.
- A style of handwriting based on that used on such prints; English round hand.
- To engrave on and print from a copperplate.