Synonyms and related words :
behind closed doors, behind the curtain, behind the scenes, behind the veil, by stealth, confidentially, covertly, furtively, hugger-mugger, in a corner, in a whisper, in camera, in darkness, in hidlings, in secret, in the background, in the dark, mysteriously, nobody the wiser, on the quiet, on the sly, privately, privily, quietly, slyly, sotto voce, stealthily, sub rosa, surreptitiously, under the breath, under the rose, undercover, underground, with bated breath