The most common and most likely answer to this crossword clue is the 8 letter word OPTATIVE
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More clues leading to the result OPTATIVE
Buddy explains!

The straight part
We know that "Expressing a wish" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case expressing a wish = optative.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 OPTATIVE mean?
OPTATIVE noun- (grammar) A mood of verbs found in some languages (e.g. Sanskrit, Old Prussian, Ancient Greek), used to express a wish. English does not have inflectional optative forms.
- (grammar) A verb or expression in the optative mood.
- Expressing a wish or a choice.
- (grammar) Related or pertaining to the optative mood.