The most common and most likely answer to this crossword clue is the 10 letter word PATHFINDER
I've seen this crossword clue in The Daily Telegraph
P
A
T
H
F
I
N
D
E
R
More clues leading to the result PATHFINDER
Buddy explains!
The straight part
We know that "pioneer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pioneer = pathfinder.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 PATHFINDER mean?
PATHFINDER noun- One who discovers a way or path; one who explores untraversed regions.
- One who first does something; a pioneer.