Emily Dickinson Lexicon

SIL'LY, a. [I have not found this word in any other language, but the Sax. asealcan signifies to be dull, inert, lazy. This corresponds with the Ar. كَسِلَ kasela, to be stupid, Heb. כסל. This may be radically the same word, with a prefix. Class Sl, No. 26.]

1. Weak in intellect; foolish; witless; destitute of ordinary strength of mind; simple; as, a silly man; a silly child.
2. Proceeding from want of understanding or common judgment; characterized by weakness or folly; unwise; as, silly thoughts; silly actions; a silly scheme; writings stupid or silly.
3. Weak; helpless. After long storms – / With which my silly bark was toss'd. [Obs.] – Spenser.