The Collaborative International Dictionary of English v.0.48:

Vernacular \Ver*nac"u*lar\, a. [L. vernaculus born in one's
   house, native, fr. verna a slave born in his master's house,
   a native, probably akin to Skr. vas to dwell, E. was.]
   Belonging to the country of one's birth; one's own by birth
   or nature; native; indigenous; -- now used chiefly of
   language; as, English is our vernacular language. "A
   vernacular disease." --Harvey.
   [1913 Webster]

         His skill in the vernacular dialect of the Celtic
         tongue.                                  --Fuller.
   [1913 Webster]

         Which in our vernacular idiom may be thus interpreted.
                                                  --Pope.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Vernacular \Ver*nac"u*lar\, n.
   The vernacular language; one's mother tongue; often, the
   common forms of expression in a particular locality, opposed
   to literary or learned forms.
   [1913 Webster + PJC]

WordNet (r) 3.0 (2006):

vernacular
    adj 1: being or characteristic of or appropriate to everyday
           language; "common parlance"; "a vernacular term";
           "vernacular speakers"; "the vulgar tongue of the masses";
           "the technical and vulgar names for an animal species"
           [syn: common, vernacular, vulgar]
    n 1: a characteristic language of a particular group (as among
         thieves); "they don't speak our lingo" [syn: slang,
         cant, jargon, lingo, argot, patois, vernacular]
    2: the everyday speech of the people (as distinguished from
       literary language)

Moby Thesaurus II by Grady Ward, 1.0:

148 Moby Thesaurus words for "vernacular":
   Babbittish, Philistine, aboriginal, accustomed, ancient language,
   argot, austerity, autochthonous, average, baldness, bareness,
   bourgeois, campy, candor, cant, classical language, colloquial,
   colloquial speech, colloquial usage, colloquialism, common,
   common speech, commonplace, confined, conventional, conversational,
   conversationalism, current, customary, dead language, directness,
   easy, endemic, everyday, familiar, frankness, general,
   geographically limited, gibberish, gobbledygook, habitual,
   high-camp, homebred, homegrown, homely, homespun, household,
   household words, idiom, illiterate speech, indigenous, informal,
   informal English, informal language, informal speech, insular,
   jargon, kitschy, language, leanness, limited, lingo,
   living language, local, localized, low-camp, matter-of-factness,
   mother tongue, mumbo jumbo, natal, native, native language,
   native speech, native tongue, native-born, naturalness,
   nonstandard, normative, of a place, openness, ordinary, original,
   parent language, parochial, patois, patter, phraseology, plain,
   plain English, plain speaking, plain speech, plain style,
   plain words, plainness, plebeian, pop, popular, predominating,
   prescriptive, prevailing, primitive, prosaicness, prosiness,
   provincial, public, regional, regular, regulation, restrainedness,
   rustic style, scatology, severity, simple, simpleness, simplicity,
   slang, soberness, spareness, speech, spoken, spoken language,
   standard, starkness, stock, straightforward, straightforwardness,
   substandard, substandard language, taboo language, talk, topical,
   unadorned style, unadornedness, unaffectedness, uneducated,
   unimaginativeness, universal, unliterary, unpoeticalness,
   unstudied, usual, vernacularism, vocabulary, vulgar,
   vulgar language, vulgar tongue, vulgate, wonted