"Merely glimpsed" is a phrase that describes catching a fleeting sight or a passing glance of something. Some synonyms that can be used to replace this phrase include "barely caught sight of," "fleetingly noticed," "momentarily viewed," "briefly perceived," and "scarcely discerned." These synonyms convey a sense of speed and brevity, indicating that the object or person being observed was seen only briefly or in passing. Other possible synonyms for "merely glimpsed" include "casually beheld," "lightly caught a glimpse of," and "fleetly scanned," each of which conveys a slightly different shade of meaning while preserving the sense of a brief and fleeting observation.