The most common and most likely answer to this crossword clue is the 8 letter word SECRETLY
S
E
C
R
E
T
L
Y
More clues leading to the result SECRETLY
- Instant deposit finally accepted by bank in confidence
- Second tyre burst, with learner inside, behind closed doors
- Moment before closure of account in bank behind closed doors
- Undercover detective leaves criminal discreetly
- Second time in bank, behind closed doors
- After short time, deposit finally put in bank, under the counter
- Undercover detective leaving discreetly out the window
- Cunningly erects laboratory’s fences under the hood
- . Let's cry about taking drug without anyone knowing
- I'd left discreetly, oddly discreetly
Buddy explains!

The straight part
We know that "behind closed doors" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case behind closed doors = secretly.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 SECRETLY mean?
SECRETLY adverb- In secret, covertly.