Is it ensure, insure, or assure?
early 13c., from Old French dragon, from Latin draconem (nominative draco) "huge serpent, dragon," from Greek drakon (genitive drakontos) "serpent, giant seafish," apparently from drak-, strong aorist stem of derkesthai "to see clearly," from PIE *derk- "to see." Perhaps the literal sense is "the one with the (deadly) glance."
The young are dragonets (14c.). Obsolete drake "dragon" is an older borrowing of the same word. Used in the Bible to translate Hebrew tannin "a great sea-monster," and tan, a desert mammal now believed to be the jackal.
(1.) Heb. tannim, plural of tan. The name of some unknown creature inhabiting desert places and ruins (Job 30:29; Ps. 44:19; Isa. 13:22; 34:13; 43:20; Jer. 10:22; Micah 1:8; Mal. 1:3); probably, as translated in the Revised Version, the jackal (q.v.). (2.) Heb. tannin. Some great sea monster (Jer. 51:34). In Isa. 51:9 it may denote the crocodile. In Gen. 1:21 (Heb. plural tanninim) the Authorized Version renders "whales," and the Revised Version "sea monsters." It is rendered "serpent" in Ex. 7:9. It is used figuratively in Ps. 74:13; Ezek. 29:3. In the New Testament the word "dragon" is found only in Rev. 12:3, 4, 7, 9, 16, 17, etc., and is there used metaphorically of "Satan." (See WHALE.)