step-

a prefix denoting connection between members of a family by the remarriage of a parent and not by blood: stepbrother.

Origin of step-

Middle English; Old English stēop-; cognate with German stief-, Old Norse stjūp- step-; akin to Old English āstēpan to bereave, bestēpan to deprive (of children)

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for step-

step-

combining form

indicating relationship through the previous marriage of a spouse or parent rather than by bloodstepson; stepfather

Word Origin for step-

Old English stēop-; compare āstӯpan to bereave

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for step-

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" (cf. 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- (see steep (adj.)).

Etymologically, a stepfather or stepmother is one who becomes father or mother to an orphan, but the notion of orphanage faded in 20c. For sense evolution, cf. Latin privignus "stepson," related to privus "deprived."