The most common and most likely answer to this crossword clue is the 4 letter word NEAP
I've seen this crossword clue in Independent
N
E
A
P
Buddy explains!
The straight part
We know that "of one apt to avoid extremes? (4)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case of one apt to avoid extremes? (4) = neap.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 NEAP mean?
NEAP noun- The tongue or pole of a cart or other vehicle drawn by two animals.
- A neap tide.
- To trap a ship (or ship and crew) in water too shallow to move, due to the smaller tidal range occurring in a period of neap tides.
- To ooze, to sink, to subside, to tail
- (of a tide) Low; lowest; the ebb or lowest point of a tide.
- Designating a tide which occurs just after the first and third quarters of the moon, when there is the least difference between high tide and low tide.
- The swede (rutabaga), called "turnip" in Scotland.