banal (= pedestrian and uninteresting for lack of new ideas) is pronounced /bə-nahl/, /bə-nal/, or /bay-nəl/. It's "a word of many pronunciations, each of which has its outspoken and often intractable proponents." [Quoting Charles Harrington Elster, The Big Book of Beastly Mispronunciations, 2d ed. (2005).]
(Bryan A. Garner, Garner's Modern English Usage, 4th ed. [New York: Oxford University Press, 2016], 94)
Note from KBJ: The three pronunciations are not equally defensible. The word "banality" is pronounced /bə-nal-ity/, not /bə-nahl-ity/ or /bay-nəl-ity/. Why would there be different pronunciations of "banal" and "banality"? To remember the pronunciation, think of the man's name "Al."
