Kenneth G. Wilson (1923). The Columbia Guide to Standard American English. 1993.
ne plus ultra (n.)
is a Latin tag literally meaning no more beyond and used today to mean the highest or best or farthest development or progress possible. There is nothing better than a ne plus ultra. Italicize it, and pronounce it either NAI or NEE PLUHS or PLOOS UHL-truh or OOL-truh. See FOREIGN PHRASES.