The word "gerth" is an uncommon word that refers to a type of girth or harness used to secure a saddle on a horse. It is spelled with a "th" at the end which indicates an unvoiced dental fricative sound, /θ/. So, the correct pronunciation of "gerth" would be /ɡɜːrθ/. Although it may not be a commonly used word, it is important to know the correct spelling and pronunciation of unique terms within various fields such as equestrianism.