The most common and most likely answer to this crossword clue is the 5 letter word ZONAL
Z
O
N
A
L
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The straight part
We know that "of a region" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case of a region = zonal.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 ZONAL mean?
ZONAL adjective- Divided into zones.
- Related to, associated with, or similar to zones.
- (of air or ocean currents) roughly longitudinal (east to west, or west to east)