—used to question a person's character or authority
—used after a noun or pronoun to show which group of people you are talking about
Full Definition of WHO
: what or which person or persons —used as an interrogative <who was elected?><find out who they are> —used by speakers on all educational levels and by many reputable writers, though disapproved by some grammarians, as the object of a verb or a following preposition <who did I see but a Spanish lady — Padraic Colum><do not know who the message is from — G. K. Chesterton>
—used as a function word to introduce a relative clause ; used especially in reference to persons <my father, who was a lawyer> but also in reference to groups <a generation who had known nothing but war — R. B. West> or to animals <dogs who…fawn all over tramps — Nigel Balchin> or to inanimate objects especially with the implication that the reference is really to a person <earlier sources who maintain a Davidic ancestry — F. M. Cross> ; used by speakers on all educational levels and by many reputable writers, though disapproved by some grammarians, as the object of a verb or a following preposition <a character who we are meant to pity — Times Literary Supplement>
— as who
archaic: as one that : as if someone
— as who should say
archaic: so to speak
— who is who or who's who or who was who
: the identity of or the noteworthy facts about each of a number of persons
Observers of the language have been predicting the demise of whom from about 1870 down to the present day <one of the pronoun cases is visibly disappearing—the objective case whom — R. G. White (1870)><whom is dying out in England, where “Whom did you see?” sounds affected — Anthony Burgess (1980)>. Our evidence shows that no one—English or not—should expect whom to disappear momentarily; it shows every indication of persisting quite a while yet. Actual usage of who and whom—accurately described at the entries in this dictionary—does not appear to be markedly different from the usage of Shakespeare's time. But the 18th century grammarians, propounding rules and analogies, rejecting other rules and analogies, and usually justifying both with appeals to Latin or Greek, have intervened between us and Shakespeare. It seems clear that the grammarians' rules have had little effect on the traditional uses. One thing they have accomplished is to encourage hypercorrect uses of whom<whom shall I say is calling?>. Another is that they have made some people unsure of themselves <said he was asked to step down, although it is not known exactly who or whom asked him — Redding (Connecticut) Pilot>.
That, which, who: In current usage that refers to persons or things, which chiefly to things and rarely to subhuman entities, who chiefly to persons and sometimes to animals. The notion that that should not be used to refer to persons is without foundation; such use is entirely standard. Because that has no genitive form or construction, of which or whose must be substituted for it in contexts that call for the genitive.
That, which: Although some handbooks say otherwise, that and which are both regularly used to introduce restrictive clauses in edited prose. Which is also used to introduce nonrestrictive clauses. That was formerly used to introduce nonrestrictive clauses; such use is virtually nonexistent in present-day edited prose, though it may occasionally be found in poetry.
Origin of WHO
Middle English, from Old English hwā; akin to Old High German hwer, interrog. pron., who, Latin quis, Greek tis, Latin qui, relative pron., who