"witches' sabbath," a midnight meeting supposed to have been held annually by demons, sorcerers, and witches under the leadership of Satan, to celebrate their orgies, 1650s, a special application of the French form of Sabbath (q.v.).
mid-15c., "belonging exclusively to one person," also "special, particular," from Old French peculiaire and directly from Latin peculiaris "of one's own (property)," from peculium "private property," literally "property in cattle" (in ancient times the most important form of property), from pecu "cattle, flock," related to pecus "cattle" (see pecuniary).
The meaning "unusual, uncommon, odd" is by c. 1600 (earlier "distinguished, special, particular, select," 1580s; for sense development, compare idiom). The euphemistic phrase peculiar institution for U.S. slavery is by 1838. Related: Peculiarly.
as a noun, in biology, "genetic variant of an animal," 1955; as a verb, in cinematic special effects, c. 1987, short for metamorphosis. Related: Morphed; morphing. Earlier it was a slang shortening of morphine (1912).
"knowledge," especially "special knowledge of spiritual mysteries," 1703, from Greek gnōsis "a knowing, knowledge; a judicial inquiry, investigation; a being known," in Christian writers, "higher knowledge of spiritual things," from PIE *gnō-ti-, from root *gno- "to know."