Old English hwær, hwar "at what place," from Proto-Germanic adverb *hwar (source also of Old Saxon hwar, Old Norse hvar, Old Frisian hwer, Middle Dutch waer, Old High German hwar, German wo, Gothic hvar "where"), equivalent to Latin cur, from PIE root *kwo-, stem of relative and interrogative pronouns. Where it's at attested from 1903.
It has figured in a great many prepositional and adverbial compounds through the years; in addition to the ones listed in this dictionary (whereas, wherefore, whereabouts, etc.) English has or had whereagainst, wherefrom, wherehence, whereinsoever, whereinto, wheremid, whereout, whereover, whereso, wheresoever, wherethrough, whereto, whereunder, whereuntil.
Daddy-long-legs is from 1814 in Britain as "crane-fly," a slender, long-legged summer fly. In the U.S., it was used by 1865 as the word for a spider-like arachnid with a small round body and very long, slender legs.
A superstition obtains among our cow-boys that if a cow be lost, its whereabouts may be learned by inquiring of the Daddy-Long-legs (Phalangium), which points out the direction of the lost animal with one of its fore legs. [Frank Cowan, "Curious Facts in the History of Insects, Including Spiders and Scorpions," Philadelphia, 1865]
1809, "bell attached to the neck of a cow to indicate her whereabouts" (usually oblong and of a heavy, clanking tone), from cow (n.) + bell (n.). They are cut from sheet metal (mostly copper, or iron coated with bronze) and folded into shape. As a musical instrument (without the clapper) by 1919; in that period associated with, and scorned as an absurdity of, jazz.
Art is long and time is fleeting,
And the man who cannot play,
On a cowbell wildly beating,
Calls it "jazz"—and gets away.
[from "The Psalm of Jazz," Oregon Voter, Aug. 30, 1919]
But an article on cowbells in "Hardware" magazine for Dec. 25, 1897, notes: "Cowbells are made in ten sizes, whose sounds range through an octave. Sometimes musical entertainers who play upon bells of one sort and another come to the manufacturer, and by selection among bells of the various sizes find eight bells that are accurate in scale."