Is it ensure, insure, or assure?
c.1735, from Late Latin bronchus, from Greek bronkhos "windpipe, throat" (from PIE *gwronkh-, from root *gwere- "to swallow") + -al (1). bronchial tubes is from 1847.
bronchial bron·chi·al (brŏng'kē-əl)adj. Relating to the bronchi, the bronchial tubes, or the bronchioles.