The Collaborative International Dictionary of English v.0.48:

Sunbeam \Sun"beam`\, n. [AS. sunnebeam.]
   A beam or ray of the sun. "Evening sunbeams." --Keble.
   [1913 Webster]

         Thither came Uriel, gliding through the even
         On a sunbeam.                            --Milton.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sunbeam
    n 1: a ray of sunlight [syn: sunbeam, sunray]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "sunbeam":
   broad day, dawn, day, day glow, daylight, dayshine, daytide,
   daytime, dusk, full sun, green flash, light of day, midday sun,
   noonlight, noontide light, ray of sunshine, shine, sun spark,
   sunbreak, sunburst, sunlight, sunshine, twilight