(Northern English) Sulky, moody.
Early 20th century: from dialect mard ‘spoilt’ (describing a child), alteration of marred (see mar).
“If you’re going to be mardy about it I won’t take you!”
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