Something that is momentary lasts for a very short period of time, for example for a few seconds or less. a momentary lapse of concentration = brief. continuing for a very short time = brief
Done in a moment; continuing only a moment; lasting a very short time; as, a momentary pang
lasting for a markedly brief time; "a fleeting glance"; "fugitive hours"; "rapid momentaneous association of things that meet and pass"; "a momentary glimpse"