Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
21st is an adjective meaning "coming next after the twentieth in position". It carries one recorded sense.
coming next after the twentieth in position
Definitions, synonyms and semantic relations for 21st come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.