The word "acetaminophen" is pronounced as: In American English: /əˌsiː.t̬əˈmɪn.ə.fən/ — sounding like "uh-see-tuh-MIN-uh-fen."
In British English: /əˌsiː.təˈmɪn.ə.fən/ — similar but with a clear "t" sound instead of the American "t̬" (flapped t).

A useful way to break it down by syllables for pronunciation is: uh-see-ta-mi- no-phen.