From Middle English who, hwo, huo, wha, hwoa, hwa, from Old English hwā (dative hwām, genitive hwæs), from Proto-Germanic *hwaz, from Proto-Indo-European *kʷos, *kʷis. Spelling change hw > wh in Middle English (without sound change in initial consonant cluster), while sound change /hw/ > /h/ due to wh-cluster reduction after a bizarre instance of three consecutive vowel shifts of /aː/ to /ɔː/ to /oː/ in Middle English. Compare how, which underwent this change earlier (in Old English), and thus is spelt h.
- (interrogative pronoun) What person or people; which person or people (used in a direct or indirect question).
- Who is that? (direct question)
- I don't know who it is. (indirect question)
- (relative pronoun) The person or people that.
- It was a nice man who helped us.
Who is a subject pronoun. Whom is an object pronoun. To determine whether a particular sentence uses a subject or an object pronoun, rephrase it to use she/he or her/him instead of who, whom; if you use she, then you use the subject pronoun who; if you use her, then you use the object pronoun.
In informal writing and speech who is also used as an object pronoun (hence one hears not only whom are you waiting for? but also who are you waiting for?), and whom may be seen as (overly) formal. As an exception to this, fronted prepositional phrases almost always use whom, e.g. one usually says with whom did you go?, not *with who did you go?.
The use of who as an object pronoun is proscribed by many authorities.
When “who” (or the other relative pronouns “that” and “which”) is used as the subject of a relative clause, the verb agrees with the antecedent of the pronoun. Thus “I who am...”, “He who is...”, “You who are...”, etc.
who (plural whos)
- A person under discussion; a question of which person.
2008 March 21, The New York Times, “Movie Guide and Film Series”, in New York Times:
- A wham-bam caper flick, efficiently directed by Roger Donaldson, that fancifully revisits the mysterious whos and speculative hows of a 1971 London bank heist.