declarant (n.)

"one who makes a declaration," 1680s, from French déclarant, from Latin declarantem (nominative declarans), present participle of declarare  "make clear, reveal, disclose, announce," from de-, here probably an intensive prefix (see de-) + clarare "clarify," from clarus "clear" (see clear (adj.)). Especially in law, "one whose admission or statement is sought as evidence."