What is "step-"

Step- \Step-\ [AS. ste['o]p-; akin to OFries. stiap-, stiep-, D. & G. stief-, OHG. stiuf-, Icel. stj?p-, Sw. styf-, and to AS. [=a]st[=e]pan, [=a]ste['o]pan, to deprive, bereave, as children of their parents, OHG. stiufen.] A prefix used before father, mother, brother, sister, son, daughter, child, etc., to indicate that the person thus spoken of is not a blood relative, but is a relative by the marriage of a parent; as, a stepmother to X is the wife of the father of X, married by him after the death of the mother of X. See Stepchild, Stepdaughter, Stepson, etc.

Old English steop-, with connotations of "loss," in combinations like steopcild "orphan," related to astiepan, bestiepan "to bereave, to deprive of parents or children," from Proto-Germanic *steupa- "bereft" (cognates: Old Frisian stiap-, Old Norse stjup-, Swedish styv-, Middle Low German stef-, Dutch stief-, Old High German stiof-, German stief-), literally "pushed out," from PIE *steup-, from root *(s)teu- (1) "to push, stick, knock," with derivatives referring to fragments (see steep (adj.)). Barnhart suggests the forms in -f- are by assimilation of the first sound in following words for "father."\n

\nEtymologically, a stepfather or stepmother is one who becomes father or mother to an orphan, but the notion of orphanage faded in 20c. and came to denote simply relation through marriage. For sense evolution, compare Latin privignus "stepson," related to privus "deprived." Compare orphan (n.).

pre. A prefix used before ''father'', ''mother'', ''brother'', ''sister'', ''son'', ''daughter'', ''child'', and so forth, to indicate that the person being identified is not a blood relative but is related through the marriage of a parent.