Whom

wiktionary

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From Middle English whom, wham, from Old English hwām, hwǣm, from Proto-Germanic *hwammai, dative case of *hwaz(“who, what”). Cognate with Scots wham(“whom”), German wem(“whom, to whom”), Danish hvem(“who, whom”), Swedish vem(“who, whom”).

etymonline

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whom (pron.)

objective case of who, Old English hwam (Proto-Germanic *hwam), dative form of hwa (from PIE root *kwo-, stem of relative and interrogative pronouns). Ungrammatical use of who form whom is attested from c. 1300.