The spelling of the word "yaw-root" is determined by its phonetics. According to the International Phonetic Alphabet (IPA), the word is pronounced as /jɔːrʊt/. The pronunciation guide indicates that the first syllable /jɔː/ is pronounced with an open-mid back rounded vowel, similar to the sound produced when pronouncing "o" in "more". The second syllable /rʊt/ is pronounced with a close back rounded vowel similar to the sound produced when pronouncing "oo" in "shoot".
Stillingia.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.