Silly

Silly, weakly foolish, stupid. This is the current sense of a word which has much changed its meaning. The O.E. selig  (usually geilelig) meant prosperous, happy, and was formed from sr?l, time, season, hence happiness, cf. Icel. stela, bliss; Ger. selig, blessed, happy, &c., probably also allied to Lat. salvus, whole, safe. The development of meaning is happy, blessed, innocent or simple, thence helpless, weak, and so foolish. The old provincial and Scottish word for a caul was "sillyhow," i.e. " lucky cap." The development of meaning of "simple," literally "onefold" (Lat. simplex), plain, artless, hence unlearned, foolish, is somewhat parallel. A special meaning of "simple," in the sense of medicinal herbs, is due to the supposition that each herb had its own particular or simple medicinal value.