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