Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
ahorseback is an adjective and adverb meaning "traveling on horseback". It carries 2 recorded senses.
on the back of a horse
“he rode horseback to town”
“managed to escape ahorse”
“policeman patrolled the streets ahorseback”
Definitions, synonyms and semantic relations for ahorseback come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.