The Collaborative International Dictionary of English v.0.48:

Scholiast \Scho"li*ast\, n. [Gr. ?, fr. ? a scholium: cf. F.
   scoliate. See Scholium.]
   A maker of scholia; a commentator or annotator.
   [1913 Webster]

         No . . . quotations from Talmudists and scholiasts . .
         . ever marred the effect of his grave temperate
         discourses.                              --Macaulay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

scholiast
    n 1: a scholar who writes explanatory notes on an author
         (especially an ancient commentator on a classical author)

Moby Thesaurus II by Grady Ward, 1.0:

64 Moby Thesaurus words for "scholiast":
   allegorist, annotator, book reviewer, captious critic, carper,
   caviler, censor, censurer, cicerone, clarifier, cognoscente,
   commentator, commenter, connoisseur, critic, criticaster,
   criticizer, critickin, criticule, cryptanalyst, cryptographer,
   cryptologist, decoder, definer, demonstrator, demythologizer,
   diaskeuast, dragoman, editor, editorial writer, editorialist,
   emendator, emender, euhemerist, exegesist, exegete, exegetist,
   explainer, explicator, exponent, expositor, expounder, faultfinder,
   glossarist, glossographer, go-between, guide, hermeneut,
   interpreter, leader writer, lexicographer, literary critic,
   man of letters, metaphrast, muckraker, news analyst, oneirocritic,
   paraphrast, publicist, reviewer, smellfungus, social critic,
   textual critic, translator