From Proto-Indo-European *ḱorh₂u, *ḱr̥h₂-no-, both from Proto-Indo-European *ḱerh₂- (“horn”). Cognate with English horn, hirn; Ancient Greek κρᾱνίον (krāníon, “skull”), κέρας (kéras, “horn”); Sanskrit शृङ्ग (śṛṅgá, “horn, tusk”). See also cerebrum (“brain”), cervus (“deer”).

cornū n (genitive cornūs); fourth declension

a horn, antler
a tusk
the horns of the moon
an arm or wing of an army
(music) a horn as a musical instrument
any substance like the material of a horn, such as the bill of a bird
the end of a book or scroll, usually made of ivory
(figuratively) power, strength, might