The most common and most likely answer to this crossword clue is the 6 letter word HARDLY
I've seen this crossword clue in Independent
H
A
R
D
L
Y
More clues leading to the result HARDLY
- Destroying Hydra around lake only with great difficulty
- Not quite daring to cross lake
- Writer has room for learner? Only just
- Just novel ultimately penned by English author
- Novelist and poet would drink litre only with great difficulty
- Line penned by author with difficulty
- Just Oliver eating last of gruel
- Oliver eating end of meal? Not quite!
- Hot lady dancing without Romeo! Not quite
- Line nailed by author, only just
Buddy explains!

The straight part
We know that "Only just" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case only just = hardly.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 HARDLY mean?
HARDLY adverb- (manner) Firmly, vigorously, with strength or exertion.
- (manner) Harshly, severely; in a hard manner.
- With difficulty.
- (degree) Barely, only just, almost not.
- Not really.