The most common and most likely answer to this crossword clue is the 2 plus 4 letter word IF ONLY
I've seen this crossword clue in The Daily Telegraph
I
F
O
N
L
Y
More clues leading to the result IF ONLY
- One’s smart about working — I wish it were true
- I tear around centre of Bonn in my dreams
- I wish one running entered into race
- I affectionately will wave goodbye to daughter, giving an expression of regret
- Would that old bats fly in circles!
- Expression of regret from one in indulgent mode losing daughter
Buddy explains!
The straight part
We know that "expression of regret" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case expression of regret = if only.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.