Part of speech: Adverb
in secrecy
Example: they did it all hugger-mugger
Topsy-turvy, Disorderly, Hole-and-corner, Clandestine, Cloak-and-dagger
The word "hugger-mugger" comes from Irish cogair. Many other languages have similar words:
Shakespeare alone introduced over 1,700 new words to English—many we still use today!