The spelling of the word "isthmiate" is derived from the noun "isthmus", which refers to a narrow strip of land that connects two larger land masses. The suffix -ate is added to form the adjective form. The correct pronunciation of this word is /ɪsθmiːət/ (ISS-mee-ate), with the stress on the second syllable. Breaking it down phonetically: the "is" is the short "i" sound, and the "thm" is pronounced with a soft "th" sound followed by a short "m" sound. Lastly, the "ate" is pronounced as "ate" in "mate".