The most common and most likely answer to this crossword clue is the 6 letter word OX-EYE
I've seen this crossword clue in The Times
O
X
-
E
Y
E
Buddy explains!

The straight part
We know that "small window" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case small window = ox-eye.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 OX-EYE mean?
OX-EYE noun- Several daisy-like flowers in various genera,
- Any oxeye daisy.
- The corn camomile (Anthemis arvensis).
- A titmouse, especially the great titmouse (Parus major) or the blue titmouse (Parus caeruleus).
- The dunlin (Calidris alpina)
- A fish Boops boops; the bogue, or box.