The Collaborative International Dictionary of English v.0.48:

Blithesome \Blithe"some\ (-s[u^]m), a.
   Cheery; gay; merry.
   [1913 Webster]

         The blithesome sounds of wassail gay.    --Sir W.
                                                  Scott.
   [1913 Webster] -- Blithe"some*ly, adv. --
   Blithe"some*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

blithesome
    adj 1: carefree and happy and lighthearted; "was loved for her
           blithe spirit"; "a merry blithesome nature"; "her
           lighthearted nature"; "trilling songs with a lightsome
           heart" [syn: blithe, blithesome, lighthearted,
           lightsome, light-hearted]

Moby Thesaurus II by Grady Ward, 1.0:

43 Moby Thesaurus words for "blithesome":
   beaming, blithe, boon, bright, bright and sunny, cheerful, cheery,
   elated, eupeptic, euphoric, exalted, exhilarated, festive, flushed,
   gay, genial, glad, gladsome, gleeful, glowing, happy, high,
   hopeful, in good spirits, in high spirits, irrepressible, jocund,
   jolly, jovial, laughing, lighthearted, of good cheer, optimistic,
   pleasant, radiant, riant, rosy, sanguine, sanguineous, smiling,
   sparkling, sunny, winsome