Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
18th is an adjective meaning "coming next after the seventeenth in position". It carries one recorded sense.
coming next after the seventeenth in position
Definitions, synonyms and semantic relations for 18th come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.