The most common and most likely answer to this crossword clue is the 10 letter word RHAPSODISE
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The straight part
We know that "To talk with enthusiasm" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to talk with enthusiasm = rhapsodise.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 RHAPSODISE mean?
RHAPSODISE verb- To speak with exaggerated or rapturous enthusiasm (about, (up)on or over something).
- To say (something) with exaggerated or rapturous enthusiasm.
- To recount or describe (something) as a rhapsody, or in the manner of a rhapsody.
- To perform a rhapsody.