raster (n.)

"a rodent mammal" 1835 (as an adjective 1833), from Modern Latin Rodentia, the order name, from Latin rodentem (nominative rodens), "the gnawers," present participle of rodere "to gnaw, eat away," which is of uncertain etymology, possibly is from an extended form of PIE root *red- "to scrape, scratch, gnaw." Uncertain connection to Old English rætt (see rat (n.)). They are characterized by having no canine teeth and strong incisors.

1883, from French rastaquouère, rastacouère (19c.) "social intruder, upstart" (especially one of exaggerated manners and dress, from a Mediterranean or South American country), thus "dashing but untrustworthy foreigner" [OED].

Short form rasta is attested from 1905. According to French sources, the word is from South American Spanish rastacuero "upstart," from arrastrar "to drag, pull, tow, trail along the ground" + cuero "leather." Arrastrar is said to be from Spanish rastro "rake," from Latin rastrum (see raster), while cuero is from Latin corium (see corium).

*rēd-, Proto-Indo-European root meaning "to scrape, scratch, gnaw."

It forms (possibly) all or part of: abrade; abrasion; corrode; corrosion; erase; erode; erosion; radula; rascal; rase; rash (n.) "eruption of small red spots on skin;" raster; rat; raze; razor; rodent; rostrum; tabula rasa.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit radati "scrapes, gnaws," radanah "tooth;" Latin rodere "to gnaw, eat away," radere "to scrape;" Welsh rhathu "scrape, polish."