L. senex, senis  old person (i.e. querulous, white-haired).
● (syn. Circaetus Ϯ Short-toed Eagle C. gallicus) "I, therefore, propose to retain Spix's genus, Milvago, for all those Polyborinæ which possess rounded nostrils with an elevated bony tubercle in the centre. They were once considered to form three distinct genera, viz. - Milvago, Spix. (Polyborus, Vieill.  Haliaëtus, Cuv.  Aquila, Meyen.)  -  Senex, Gray. (Circaëtus, Less.)  - Phalcobænus, D'Orb. but a careful comparison of the several species, shows a regular gradation in structure from one to the other, which induces me to consider them as only forming two sections of one genus" (G. Gray in Darwin 1839).
● (syn. Phalcoboenus Ϯ Striated Caracara P. australis) "SENEX, Gray.  -  Like the former [Milvago], but of a larger size, with the bill longer, and the culmen less elevated, but rounded.  S. Australis, Gray.  ...  My brother proposed to place the genus Senex and its allies with the Noble Falcons, as they have the same formed nostrils; and he now considers that it shows at least an affinity to the birds of that group" (J. Gray in Jardine & Selby 1839).

Search for more names on the Key to Scientific Names in Ornithology by James A. Jobling.
Recommended citation
Jobling, J. A. (2018). Key to Scientific Names in Ornithology. In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.) (2018). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from on 15 December 2018).