diplasiasmus

from The Century Dictionary.

• noun A figure of orthography, consisting in writing a letter double which is usually written single, as, in Greek τοσσ, σ1ός for τοσός.
• noun In rhetoric, repetition of a word or name for the sake of emphasis: as,“O Jerusalem, Jerusalem, thou that killest the prophets,” Mat. xxiii. 37. Also called epizeuxis.