That's silly

The word "silly" originally meant (Old English -- approximately the 5th-12th centuries) "blessed," or "happy."

The word's considerable sense development moved from "blessed" to "pious," to "innocent" (1200), to "harmless," to "pitiable" (c.1280), to "weak" (c.1300), to "feeble in mind, lacking in reason, foolish" (1576).

Word meanings change, and that's why those old manuscripts can be confusing.

The Authorized Version ("King James Version") of the Bible is often a good marker for word meanings. In Job 5.2 ("For wrath killeth the foolish man, and envy slayeth the silly one") we have the still current meaning of silly in use. (The word "gay" hasn't fared as well from 1611 -- see James 2.3, "him that weareth the gay clothing.")