Synonyms:
- at night,
- behind the curtain,
- behind the scenes,
- behind the veil,
- benighted,
- by night,
- covertly,
- dark,
- darkling,
- in a corner,
- in a whisper,
- in darkness,
- in hidlings,
- in secret,
- in the background,
- in the night,
- nobody the wiser,
- secretly,
- sotto voce,
- sub rosa,
- under the breath,
- under the rose,
- undercover,
- underground,
- with bated breath