The most common and most likely answer to this crossword clue is the 8 letter word CARDAMON
I've seen this crossword clue in The Daily Telegraph
C
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The straight part
We know that "spice" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spice = cardamon.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.
Crossword Answer definitions
CARDAMON noun- The Elettaria cardamomum, an Indian herb.
- The seed of E. cardamomum, used as a medicine and spice, especially in curry powder.
- The seeds or seed capsules of the Aframomum melegueta, used as a medicine and spice, especially as a substitute for black pepper and in flavoring alcoholic beverages.
- The Aframomum melegueta itself, a herbaceous perennial plant native to the swamps of the West African coast.