Secret, clandestine. Alternate definition, confused, disorderly.
Early 16th century: probably related to huddle and to dialect mucker ‘hoard money, conceal’.
“He knows something and he’s being all hugger-mugger about it!”
The last stage of life; old age.
Senectitude comes from the Medieval Latin noun senectitūdō meaning “old age,” which in turn comes from Classical Latin senectūs, a derivative of the noun senex meaning “old man.” Senectitude entered English in the late 1700s, more precisely, in 1796 in Jonathan Swift’s Gulliver’s Travels