The most common and most likely answer to this crossword clue is the 4 letter word INST
I've seen this crossword clue in The Guardian
I
N
S
T
More clues leading to the result INST
- Poles invested in tech this month
- Upload photos here; losing a tiny bit of weight this month!
- … this month: partners needed to stop it
- Currently batting, openers in some trouble
- November 1st’s around this month
- The present month, in a way
- In a way, it may mean this month
- This month in a short way in a short way
- Immediate dismissal of worker at the end of this month
- This month in Westminster
Buddy explains!

The straight part
We know that "this month" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case this month = inst.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.