adjective sillier -·lier, silliest -·li·est

1. Obsolete
   1. simple; plain; innocent
   2. feeble; infirm; helpless
2. Now Rare feebleminded; imbecile
3. having or showing little sense, judgment, or sobriety; foolish, stupid, absurd, ludicrous, irrational, etc.: often used in a weakened sense to mean “unreasonably concerned” don't be silly, it's no bother
4. frivolous or trivial
5. Informal dazed or senseless, as from a blow

Etymology: ME seli, sili (with shortened vowel), good, blessed, innocent < OE sælig, happy, prosperous, blessed (akin to Ger selig, blessed) < sæl, happiness < IE base *sel-, favorable, in good spirits (> Gr hilasia, propitiation, hilaros, gay, L solari, to comfort); sense development: happy → blissful → unaware of reality → foolish

noun pl. sillies -·lies