The most common and most likely answer to this crossword clue is the 8 letter word EXTENDER
I've seen this crossword clue in The Daily Telegraph
E
X
T
E
N
D
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R
More clues leading to the result EXTENDER
Buddy explains!

The straight part
We know that "one to reach out" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one to reach out = extender.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 EXTENDER mean?
EXTENDER noun- Any of various substances designed to extend any of several properties of a material.
- Any of various components designed to extend the length of a device.
- Any substance added to food to bulk it out, with a higher protein content than a filler.
- A runner, or quick-draw. (from sense #2)
- A phrase that extends an expression to include further members of a set, e.g. "and stuff", "or something".