1530s, "loose, water-worn pebbles of the seashore," probably from a dialectal survival of Old English bece, bece "stream," according to Barnhart from Proto-Germanic *bakiz (source also of Dutch beek, German Bach, Swedish bäck "stream, brook, creek"), perhaps from PIE root *bhog- indicating flowing water.

It was extended to loose, pebbly shores (1590s), then in 17c. to "shore of the sea" generally, regardless of composition, especially the part of any shore between high and low tide marks. According to OED (1989) in dialect around Sussex and Kent beach still has the meaning "pebbles worn by the waves." French grève shows the same evolution.

Beach ball is recorded by 1940; beach bum by 1950.

fourth letter of the Roman alphabet, from Greek delta, from Phoenician and Hebrew daleth, pausal form of deleth "door," so called from its shape.

The form of the modern letter is the Greek delta (Δ) with one angle rounded. As the sign for "500" in Roman numerals, it is said to be half of CIƆ, which was an early form of M, the sign for "1,000." 3-D for "three-dimensional" is attested from 1952.

Unetymological -d- is the result of a tendency in English and neighboring languages, perhaps for euphony, to add -d- to -n-, and especially to insert or swap a -d- sound when -l- or -r- follow too closely an -n-.

Compare sound (n.1), gender (n.), thunder (n.), spindle, kindred, strand (n.2) "fiber of rope," dialectal rundel, rundle for runnel. Swound was a form of swoun (swoon) attested from mid-15c, and used by Malory, Spenser, Lyly, Middleton, Beaumont & Fletcher. Among the words from French are powder (n.), meddle, tender (adj.), remainder, also riband, jaundice. It is less evident in spider (an agent noun from the Germanic *spin- root), and perhaps explains lender in place of loaner.

"land bordering a large body of water," c. 1300, from Old English scora, sceor- (in place-names) or from Middle Low German schor "shore, coast, headland," or Middle Dutch scorre "land washed by the sea," all probably from Proto-Germanic *skur-o- "cut," from PIE root *sker- (1) "to cut."

This is the usual theory, "but the etymological notion is not easy to determine" [OED]. It has been proposed as meaning "division" between land and water, but if the word began on the North Sea coast of the continent, it might as well have meant originally "land 'cut off' from the mainland by tidal marshes" (compare Old Norse skerg "an isolated rock in the sea," related to sker "to cut, shear").

Old English words for "coast, shore" were strand (n.), waroþ, ofer. Few Indo-European languages have such a single comprehensive word for "land bordering water" (Homer uses one word for sandy beaches, another for rocky headlands).

General application to "country near a seacoast" is attested from 1610s. In law, typically the tract between the high- and low-water marks (1620s). Shore-bird is attested from 1670s; the sailor's shore-leave by 1845.