"Diehard" and "die-hard" can be used as adjectives or nouns; they can refer to a person with an unwavering belief, or describe either the person or the belief, as in "diehard fan" or "diehard fascism". The movie title instead refers to the act of "dying hard", perhaps to indicate the instance of a person or idea being diehard - difficult to put a stop to, as the idiom implies. It is not to be understood as a command. (Умереть вм. умри).