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