Late 16th century; earliest use found in Gabriel Harvey (c1552–1631), scholar and writer. From classical Latin grandiloquus using a grand or lofty style, speaking in an arrogant tone + -ous.
Definition of grandiloquous in US English:
grandiloquous
adjectiveɡranˈdɪləkwəs
rare
Grandiloquent.
Origin
Late 16th century; earliest use found in Gabriel Harvey (c1552–1631), scholar and writer. From classical Latin grandiloquus using a grand or lofty style, speaking in an arrogant tone + -ous.