Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
diagrammatically is an adverb meaning "in a diagrammatic manner". It carries one recorded sense.
in a diagrammatic manner
“the landscape unit drawn diagrammatically illustrates the gentle rolling relief, with a peat-filled basin”
Definitions, synonyms and semantic relations for diagrammatically come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.