The most common and most likely answer to this crossword clue is the 9 letter word INITIATOR
I've seen this crossword clue in The Daily Telegraph
I
N
I
T
I
A
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More clues leading to the result INITIATOR
Buddy explains!

The straight part
We know that "Starter" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case starter = initiator.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 INITIATOR mean?
INITIATOR noun- One who initiates.
- A substance that initiates a chain reaction or polymerization.
- A task (in a mainframe computer) that initiates multiple jobs.
- A material whose presence in the body eventually leads to cancer.