step-daughter n.

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" (source also of 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."

Etymologically, 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.).

Middle English doughter, from Old English dohtor "female child considered with reference to her parents," from Proto-Germanic *dokhter, earlier *dhutēr (source also of Old Saxon dohtar, Old Norse dóttir, Old Frisian and Dutch dochter, German Tochter, Gothic dauhtar), from PIE *dhugheter (source also of Sanskrit duhitar-, Avestan dugeda-, Armenian dustr, Old Church Slavonic dušti, Lithuanian duktė, Greek thygater). The common Indo-European word, lost in Celtic and Latin (Latin filia "daughter" is fem. of filius "son").

The modern spelling evolved 16c. in southern England. In late Old English also "woman viewed in some analogous relationship" (to her native country, church, culture, etc.). From c. 1200 of anything regarded as feminine, considered with respect to its source. Related: Daughterly.

Daughter-in-law is attested from late 14c. (see in-law). Old English. Earlier was sonnes wif (early 14c.), earlier still snore, from Old English snoru, cognate with Old Norse snör, archaic German Schnur, from PIE root *snuso- (source also of Sanskrit snuṣa-, Greek nyos, Latin nurus (itself the source of Old French nuere, Spanish nuera), Old Church Slavonic snŭcha, Russian snocha), which is of uncertain origin.