"grant temporary possession of," late 14c., from past tense of Old English lænan "to grant temporarily, lease out, make loans, lend money at interest," from Proto-Germanic *laihwnjan, verb derived from *loikw-nes-, the prehistoric source of Old English læn "gift" (see loan (n.)). Compare Dutch lenen, Old High German lehanon, German lehnen, all verbs derived from nouns. In Middle English the past tense form, with terminal -d, became the principal form on analogy of bend, send, etc. To lend an ear "listen" is from late 14c.

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.

"one who lends money on interest," 1765, from money + lender.