We don't have synonyms for impen yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are impel, limpen and imped.
°to be about to happen or occur, especially of something which takes some time such as a process or procedure rather than just a short event. "To impend" often has the connotation of threat.
°to be about to happen or occur, especially of something which takes some time such as a process or procedure rather than just a short event. "To impend" often has the connotation of threat.