The word "progaster" is spelled with a combination of consonants and vowels that can be a bit tricky to pronounce correctly. In IPA phonetic transcription, it is spelled /prəʊˈɡæstə/. The first syllable starts with the "p" sound, followed by "r" and "o" sounds. The "g" sound then follows, followed by the "a" and "s" sounds. Finally, the word ends with two "t" sounds and a short "uh" sound. When pronouncing "progaster," it's important to emphasize the "o" sound, and to not confuse the two "t" sounds with a single "t" sound.
Archenteron.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.