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