The most common and most likely answer to this crossword clue is the 6 letter word BARELY
I've seen this crossword clue in The Times
B
A
R
E
L
Y
More clues leading to the result BARELY
Buddy explains!

The straight part
We know that "Just" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case just = barely.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 BARELY mean?
BARELY adverb- (degree) By a small margin.
- (degree) Almost not at all.
- Merely.