word-forming element expressing incomplete resemblance (such as poetaster), usually diminutive and deprecatory, from Latin -aster, from a suffix forming nouns from verbs ending in Greek -azein; in later Latin generalized as a pejorative suffix, as in patraster "he who plays the father."

element active in English word formation from mid-18c. and meaning "star or celestial body; outer space," from Greek astro-, stem and combining form of astron "star," which is related to aster "star," from PIE root *ster- (2) "star." In ancient Greek, aster typically was "a star" and astron mostly in plural, "the stars." In singular it mostly meant "Sirius" (the brightest star).