The most common and most likely answer to this crossword clue is the 9 letter word ENDOCRINE
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The straight part
We know that "Hormone" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hormone = endocrine.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 ENDOCRINE mean?
ENDOCRINE noun- The secretion of an endocrine gland.
- An endocrine gland.
- Producing internal secretions that are transported around the body by the bloodstream.
- Pertaining to the endocrine glands or their secretions.