Covertly (8)
There are a few possibilities for this:
surreptitiously
'covertly' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for secretly that I've seen before include "Covertly" , "On the q.t" , "under cover" , "behind closed doors" , "without telling anyone" .)
(Another definition for insecret that I've seen is " Concealed".)
(Other definitions for surreptitiously that I've seen before include "not 14 [OVERTLY]" , "in secret?" .)