Occurring in or representing two distinct forms.
Mid 19th century: from Greek dimorphos (from di- ‘twice’ + morphē ‘form’) + -ic.
“In this sexually dimorphic species, only the males have wings”
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