Mid 19th century; earliest use found in Robley Dunglison (1798–1869), physician and medical writer. From classical Latin pilus hair + -eous, after osseous, carneous, etc.
Definition of pileous in US English:
pileous
adjectiveˈpʌɪlɪəs
Medicine rare
Of, relating to, or consisting of hair.
Origin
Mid 19th century; earliest use found in Robley Dunglison (1798–1869), physician and medical writer. From classical Latin pilus hair + -eous, after osseous, carneous, etc.