The spelling of the word "Calumbin" can be quite tricky if you're not familiar with the IPA phonetic transcription. In IPA, it is spelled /kʌlʌmbɪn/. The first syllable is pronounced with a short "u" sound followed by a schwa sound. The second syllable has a quick "l" sound, followed by "uh" and "m". The final syllable consists of a short "i" sound and "n". Overall, the pronunciation is similar to "kuh-luhm-bin" with a slight emphasis on the second syllable.
An amaroid, C21H24O7, from calumba, occurring in colorless needles and prisms; it is upon the presence of this that the bitterness of the crude drug depends.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.