“Undecided” was written in 1938 by Charles Shavers (1920 – 1971), with lyrics by Sid Robin (1912 – 1986).
Shaver, a big band veteran, joined the Onyx Club band in 1937. He took over the group, composing and arranging new tunes.
When Shaver sent one of his compositions to his publisher, the publisher wired back asking for the title. Shaver's response was “Undecided," which was mistakenly thought to be the title.