One who bespeaks; a person who speaks for, indicates, or orders something in advance (archaic).
From 'bespeak' plus the agent suffix '-er,' creating a noun for a person performing the action. This form is obsolete in standard English.
Most '-er' agent nouns from archaic verbs have simply vanished—you won't find 'besmircher' or 'begrudger' in modern English, showing how languages constantly prune away words for actions we no longer think of as noteworthy enough to name agents for.
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