The most common and most likely answer to this crossword clue is the 4 plus 6 letter word OPEN SESAME
I've seen this crossword clue in The Guardian
O
P
E
N
S
E
S
A
M
E
More clues leading to the result OPEN SESAME
- Key command in move against thieves
- Special way to enter competition, used by seeds
- Work may be seen with duplicate password
- Inaugurate plant that’s key to discovering riches
- Old writers mentioned before, adopting eastern magic words
- Instruction said to give one access to work seen strangely equal
- Frank’s English likewise said to gain entrance
- Old writers start to enjoy unchanged magic spell
- Public seems upset about a magic formula
- Surprisingly, a poem’s seen to offer passcode
Buddy explains!
The straight part
We know that "magic formula" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case magic formula = open sesame.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.