Thirtieth is the ordinal adjective form of thirty, used to denote the number that comes after twenty-ninth. It’s spoken with two syllables in many accents, combining the base /ˈθɜːr/ (or /ˈðɜːr/ in some dialects) with a light, final /tiːəθ/ or /tiːð/ sequence. The stress is on the first syllable; the ending cluster can sound like -teenth due to the /tiː/ + θ or /tiːð/ realization.
Full pronunciation guide
