The most common and most likely answer to this crossword clue is the 7 letter word CRYPTIC
I've seen this crossword clue in Financial Times
C
R
Y
P
T
I
C
More clues leading to the result CRYPTIC
- Vault over most of ice that’s hidden
- Hidden underground cell, leaders in international crime
- This crossword is
- Call film about tango mystifying
- Hidden clue here will be!
- Puzzling call before soft muscular contraction
- Appropriate kind of clue for this answer?
- Keen on exercise I can start in secret
- Enigmatic, keen and in charge, set about exercising
- Sob quietly, habitual response describing the Toughie?
Buddy explains!

The straight part
We know that "in secret" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case in secret = cryptic.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 CRYPTIC mean?
CRYPTIC noun- A cryptic crossword.
- Having hidden meaning.
- Mystified or of an obscure nature.
- Involving use of a code or cipher.
- Of a crossword, or a clue in such a crossword, using, in addition to definitions, wordplay such as anagrams, homophones and hidden words to indicate solutions.
- Well camouflaged; having good camouflage.
- Serving as camouflage.
- Apparently identical, but actually genetically distinct.
- Living in a cavity or small cave.