The most common and most likely answer to this crossword clue is the 8 letter word ACTUATOR
I've seen this crossword clue in The Times
A
C
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U
A
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Buddy explains!
The straight part
We know that "one initiating operation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one initiating operation = actuator.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 ACTUATOR mean?
ACTUATOR noun- Something that actuates something else, especially a usually electric device that causes a mechanical device (i.e. a mechanism) to be switched on or off, for example an electric motor that opens and closes a valve
- The mechanism that moves the head assembly on a disk drive
- A relay that controls the flow of electricity