Early 17th century; earliest use found in Thomas Shelton (fl. 1598–1629), translator. From classical Latin altisonus that sounds high up or in the heavens + -ant.
Definition of altisonant in US English:
altisonant
adjectivealˈtɪsənənt
rare
High-sounding, lofty, pompous, loud.
Origin
Early 17th century; earliest use found in Thomas Shelton (fl. 1598–1629), translator. From classical Latin altisonus that sounds high up or in the heavens + -ant.