Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
third-rater is a noun meaning "one who is third-rate or distinctly inferior". It carries one recorded sense.
one who is third-rate or distinctly inferior
Definitions, synonyms and semantic relations for third-rater come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.