The Collaborative International Dictionary of English v.0.48:

lovesong \lovesong\, love song \love song\n.
   a song about love or expressing love for another person.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

love song
    n 1: a song about love or expressing love for another person
         [syn: love song, love-song]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "love song":
   Brautlied, Christmas carol, Kunstlied, Liebeslied, Volkslied, alba,
   anthem, art song, aubade, ballad, ballade, ballata, barcarole,
   blues, blues song, boat song, bridal hymn, brindisi, calypso,
   canso, canticle, canzone, canzonet, canzonetta, carol, cavatina,
   chanson, chant, chantey, croon, croon song, dirge, ditty,
   drinking song, epithalamium, folk song, hymeneal, lay, lied, lilt,
   love-lilt, matin, minstrel song, minstrelsy, national anthem,
   prothalamium, serena, serenade, serenata, song, theme song,
   torch song, war song, wedding song