The Collaborative International Dictionary of English v.0.48:

Conversational \Con`ver*sa"tion*al\
   (k[o^]n`v[~e]r*s[=a]"sh[u^]n*al), a.
   Pertaining to conversation; in the manner of one conversing;
   as, a conversational style. --Thackeray.
   [1913 Webster]

WordNet (r) 3.0 (2006):

conversational
    adj 1: characteristic of informal spoken language or
           conversation; "wrote her letters in a colloquial style";
           "the broken syntax and casual enunciation of
           conversational English" [syn: colloquial,
           conversational]

Moby Thesaurus II by Grady Ward, 1.0:

67 Moby Thesaurus words for "conversational":
   all jaw, answering, candid, chatty, chitchatty, colloquial, common,
   communicating, communicational, communicative, communional,
   confabulatory, cozy, effusive, everyday, expansive, familiar, flip,
   fluent, frank, gabby, garrulous, gassy, glib, gossipy, gregarious,
   gushy, informal, interacting, interactional, interactive,
   intercommunicational, intercommunicative, intercommunional,
   interlocutory, interresponsive, interrogative, interrogatory,
   linguistic, long-winded, loquacious, multiloquent, multiloquious,
   newsy, nonstandard, oral, overtalkative, prolix, questioning,
   responsive, smooth, sociable, speech, spoken, substandard,
   talkative, talky, telepathic, transmissional, uneducated,
   unliterary, unstudied, verbal, verbose, vernacular, voluble,
   windy