"Shadowed" (adjective/verb) derives from the Middle English schadowen (mid-14th century), originating from the Old English sceadwian ("to protect", "to overspread with shade").  It shares roots with the noun "shadow," originating from Proto-Germanic skaduz and the Proto-Indo-European root *(s)ḱeh₃- ("darkness").  It means to be darkened, protected, or followed.  "Shadowed" typically refers to an area in shade or a person followed secretly (as in surveillance). 

According to the Oxford English Dictionary (OED), the earliest known use of the adjective shadowed is in the Middle English period (1150-1500), with the earliest evidence dating back to approximately 1400.  It appears in Secreta Secretorum in the context of "Gov. Lordsh.".  The verb shadow dates back to the Old English period (pre-1150).  The meaning of shadowed evolved from meaning "protected from sun, overspread with shade" in the mid-14th century, to "cast a shadow, or marked with light/dark gradations" in the late 14th century, to "follow like a shadow, surveillance" in the 16th century. 

Shadowed (in writing stories) is often referred to as foreshadowing or the shadow archetype—is a vital storytelling technique that serves as the "silent engine" of narrative, providing structure, tension, and thematic depth.  It acts as a bridge between the unseen (unconscious thoughts, future events) and the seen (visible actions, plot points), preventing stories from feeling contrived or abrupt.