A critical or discursive introduction to a book.
Mid 17th century: via Latin from Greek, passive present participle (neuter) of prolegein ‘say beforehand’, from pro ‘before’ + legein ‘say’.
“The essay was nothing but a length prolegomenon, designed to put you off reading the actual work.”
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