From Middle English glimeren, glemeren (“to glimmer”), equivalent to glim (“to shine”) + -er (frequentative suffix). Cognate with German Low German glimmern (“to glimmer”), German glimmern (“to glimmer”), Danish glimre (“to glimmer”), Swedish glimra (“to glimmer”). Doublet of glimpse. Sense 5 was coined in the 2020s in analogy to trigger.