Why is the ninth month called September?
"shake," c.1400, alteration of chiveren (c.1200), of uncertain origin, perhaps from Old English ceafl "jaw," on notion of chattering teeth. Spelling change of ch- to sh- is probably from influence of shake. Related: Shivered; shivering.
"to break in or into many small pieces," c.1200, from the source of shiver (n.). Chiefly in phrase shiver me timbers (1835), "a mock oath attributed in comic fiction to sailors" [OED]. My timbers! as a nautical oath (probably euphemistic) is attested from 1789 (see timber (n.)). Related: Shivered; shivering.
"small piece, splinter, fragment, chip," c.1200, perhaps from an unrecorded Old English word, related to Middle Low German schever schiver "splinter," Old High German scivero, from Proto-Germanic *skif- "split" (cf. Old High German skivaro "splinter," German Schiefer "splinter, slate"), from PIE *skei- "to cut, split" (see shed (v.)). Commonly in phrases to break to shivers "break into bits" (mid-15c.). Also, shiver is still dialectal for "a splinter" in Norfolk and Lincolnshire.
"a tremulous, quivering motion," 1727, from shiver (v.1). The shivers in reference to fever chills is from 1861.