The Collaborative International Dictionary of English v.0.48:

Belles-lettres \Belles-let"tres\, n. pl. [F.]
   Polite or elegant literature; the humanities; -- used
   somewhat vaguely for literary works in which imagination and
   taste are predominant.
   [1913 Webster] Belletristic

WordNet (r) 3.0 (2006):

belles-lettres
    n 1: creative writing valued for esthetic content [syn: belles-
         lettres, belles lettres]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "belles-lettres":
   French literature, Renaissance literature, ancient literature,
   classics, contemporary literature, erotic literature, erotica,
   folk literature, humane letters, kitsch, letters, literature,
   medieval literature, national literature, obscene literature,
   polite literature, pop literature, popular literature,
   pornographic literature, pornography, pseudonymous literature,
   republic of letters, scatological literature, serious literature,
   travel literature, underground literature, wisdom literature