Longlasting is an adjective that refers to something that lasts for a significant period of time. Some of the antonyms for longlasting include ephemeral, fleeting, momentary, transient, evanescent, impermanent, and temporary. Ephemeral refers to something that lasts for a very short time, while fleeting refers to something that quickly disappears. Momentary means that something only lasts for a moment, while transient is used to refer to something that is not permanent. Evanescent refers to something that fades away or disappears quickly, while impermanent is used to describe something that is not intended to last forever. Temporary is an adjective that refers to something that is not meant to last for a long time, and could also be used as an antonym for longlasting.