Turns out that step- is related
to step, but not as closely as you'd expect. When I was a child, my father
divorced my mother and remarried. When I referred to my father's new wife
as my "stepmother," a girlfriend objected that she didn't think that was
right unless my natural mother was dead. My friend was remarkably attuned
to the history, if not current usage, of English, since "step-" is derived
from a verb relating to orphan and is related to Gc words having to do
with bereavement. In OE, "stepchild" meant orphan. By extension, a stepparent
was the person who married a blood parent after the death of a previous
spouse. The OED still defines stepfather and stepmother by reference to
deceased parent, but not stepson or -daughter. American usage is less morbid,
allowing step- relationships to be defined solely by divorce and remarriage.
Perhaps Americans are just resigned to divorces as common--and needed to
adapt the words to deal with the relationships.
The OED, in fact, waffles in a puzzling
fashion, being uncertain whether "stepmother" or "stepchild" is the original
concept from which the remaining words developed. This seems wrong. If
orphanage, or related bereavement of any kind, is the root sense, then
stepchild must be the base word; the widowed parent's new spouse has little
to do with the bereavement.
The IE root is *steu-, which is thought to convey the idea of push or knock or beat, with the sense, in many derived words, of projecting or sticking up. Hence, "steep," "steeple." Many descendant words carry the sense of something which has been beaten on, like a drum, whence "tympanum," your ear drum, or "type," which is soft metal beaten into a hard form, or "stupid," which is someone who has been stunned, also "contuse." Other derivatives express force or effort, like "stutter," "student," "toil" (from L for hammer). It is worthy of remark that none of the words other than "step-" that come down to us suggest death or bereavement.