Most expiring can be replaced with a variety of synonyms that convey similar meanings. Some possible alternatives include: most short-lived, most ephemeral, most fleeting, most transitory, most evanescent, most impermanent, most fading, most vanishing, most perishable, most temporal, most fugacious, most passing, most momentary, and most mutable. Each of these words captures the notion of something that is fleeting, transitory, or temporary, whether in terms of its physical existence, its relevance or importance, or its ability to make an impact. As such, they can be useful in a range of contexts, from discussions of products or trends to broader philosophical conversations about the nature of existence and change.