1964, from "quas(i-stell)ar radio source" (1963); see quasi- + stellar. So called because they resembled stars in photographic images; now thought to be massive, distant, extremely luminous active galactic nuclei.
word-forming element used since 18c. (but most productively in 20c.), "kind of, like but not really, as if," expressing some resemblance but implying a degree of fictitious or unreal quality or lack of some important feature; from Latin quasi "as if, as it were" (see quasi).
1650s, "pertaining to stars, star-like," from Late Latin stellaris "pertaining to a star, starry," from stella "star," from PIE *sterla-, suffixed form of root *ster- (2) "star." Meaning "outstanding, leading" (1883) is from the theatrical sense of star.