Come to prayer! (حَيَّ عَلَى الصَّلاةِ)‎ – What type of word is ‎حَيَّ‎?‎‎

Recently a reader asked me about the word حَيَّ. The word is used in the call of the Muezzin: Come to prayer! (حَيَّ عَلَى الصَّلاةِ). The word in question – حَيَّ – is a so-called اِسْم الْفِعْل. There is no clear translation for it. In fact, we have to deal with a “hybrid”. Let’s do some analysis.