Dictionary.com
Thesaurus.com

summeriness

  • a word derived from summer.
    summer
    noun
    the season between spring and autumn, in the Northern Hemisphere from the summer solstice to the autumnal equinox, and in the Southern Hemisphere from the winter solstice to the vernal equinox.
  • a word derived from summery.
    summery
    adjective
    of, like, or appropriate for summer.