Merriam-Webster Collegiate Dictionary - silly

 adjective  (sillier; -est)  Etymology: Middle English sely, ~ happy, innocent, pitiable, feeble, from Old English s?lig, from s?l happiness; akin to Old High German salig happy  Date: 14th century  1. archaic helpless, weak  2.  a. rustic, plain  b. obsolete lowly in station ; humble  3.  a. weak in intellect ; foolish  b. exhibiting or indicative of a lack of common sense or sound judgment a very ~ mistake  c. trifling, frivolous  4. being stunned or dazed scared ~ knocked me ~  Synonyms: see simple  • sillily adverb  • silliness noun  • ~ noun or adverb