hugger-mugger (adv.)

also huggermugger, "secretly, privately," 1520s, one of a number of similar-sounding reduplicated words in use around this time and meaning much the same thing, including hucker-mucker, which may be the original of the bunch if the basis is, as some think, Middle English mukre "to hoard up, conceal." Also compare Middle English hukmuck, late 15c., name of some sort of device for cleansing.