Word Origin for blithe
Old English bliþe "joyous, kind, cheerful, pleasant," from Proto-Germanic *blithiz "gentle, kind" (cf. Old Saxon bliði "bright, happy," Middle Dutch blide, Dutch blijde, Old Norse bliðr "mild, gentle," Old High German blidi "gay, friendly," Gothic bleiþs "kind, friendly, merciful").
Rare since 16c. No cognates outside Germanic. "The earlier application was to the outward expression of kindly feeling, sympathy, affection to others, as in Gothic and ON.; but in OE. the word had come more usually to be applied to the external manifestation of one's own pleased or happy frame of mind, and hence even to the state itself." [OED]