The most common and most likely answer to this crossword clue is the 7 letter word SETTLER
I've seen this crossword clue in The Times
S
E
T
T
L
E
R
More clues leading to the result SETTLER
- Pioneer crossword compiler entertains only third of solvers
- Person arriving in country takes dog around lake
- Letters dealt out decisive blow
- Crossword compiler, about fifty, one taking up residence
- New arrival has me pinching my own bottom?
- Poins, for instance, taking in the opening of Lancaster’s decisive argument
- Dog jumping over wall finally, one occupying new territory
- Gun dog bites hand of pioneer
- Maybe referee part of tennis match, misapplying “let” rule
- Line crossed by me, not an inhabitant initially
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 = settler.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 SETTLER mean?
SETTLER noun- Someone who settles in a new location, especially one who takes up residence in a previously uninhabited place; a colonist.
- Someone who decides or settles something, such as a dispute.
- That which settles or finishes, such as a blow that decides a contest.
- The person in a betting shop who calculates the winnings.
- A drink which settles the stomach, especially a bitter drink, often a nightcap.
- A vessel, such as a tub, in which something, such as pulverized ore suspended in a liquid, is allowed to settle.