WordNet (r) 3.0 (2006):

hugger mugger
    v 1: act stealthily or secretively

Moby Thesaurus II by Grady Ward, 1.0:

110 Moby Thesaurus words for "hugger mugger":
   airtight secrecy, all over, all over hell, anarchic, arsy-varsy,
   ass-backwards, back-door, backstairs, balled up, black out,
   bollixed up, by stealth, censor, chaotic, clandestine,
   close secrecy, closeness, concealment, confused, covert, covertly,
   crypticness, discreetness, discretion, evasion, evasiveness,
   every which way, feline, fouled up, furtive, furtively,
   galley-west, harum-scarum, hash, helter-skelter, hiddenness,
   hidlings, higgledy-piggledy, hole-and-corner, hugger-muggery, hush,
   hush up, hush-hush, in a jumble, in a mess, in a muddle, in camera,
   in confusion, in disarray, in disorder, jumble, jumbled, jungle,
   kill, litter, mash, mixed up, mucked up, muddle, muddled, muffle,
   privately, privy, quash, quiet, repress, rummage, scattered,
   scramble, screwed up, secrecy, secretiveness, secretness, shifty,
   shush, silence, sit on, skimble-skamble, skulking, slinking,
   slinky, sly, smother, snafu, sneaking, sneaky, squash, squelch,
   stealthily, stealthy, stifle, sub rosa, subterfuge, suppress,
   surreptitious, surreptitiously, the dark, topsy-turvy, tumble,
   uncommunicativeness, under-the-counter, under-the-table,
   undercover, underground, underhand, underhanded, underneath,
   unobtrusive, upside-down, willy-nilly