"an animal resembling a serpent, with legs added to it" [Johnson], late 14c., lusarde, from Anglo-French lusard, Old French laisarde "lizard" (Modern French lézard), from Latin lacertus (fem. lacerta) "lizard," a word of unknown origin. The ending in French and English is probably influenced by words in -ard.
It is identical to Latin lacertum "upper arm, muscular part of the arm, from the shoulder to the elbow" (opposed to bracchium), which suggests a pattern similar to that of Latin musculus "a muscle," literally "little mouse" (diminutive of mus "mouse"), so called because the shape and movement of the biceps were thought to resemble mice. It is unclear which Latin sense, the arm-muscle or the lizard, is original. De Vaan finds the words perhaps connected to Greek likertizein "to jump, dance," which Beekes finds likely from Pre-Greek.
Run fast, stand still. This, the lesson from lizards. [Ray Bradbury]
The modern form of the English word is attested from 1620s, with unetymological -r as in tater, feller, etc. (Alligarter was an early variant) and an overall Latin appearance. The slang meaning "non-playing devotee of swing music" is attested from 1936; the phrase see you later, alligator is from a 1956 song title.
large lizard of the American tropics, 1550s, from Spanish, from Arawakan (West Indies) iguana, iwana, the local name for the lizard.
Foure footed beastes ... named Iuannas, muche lyke vnto Crocodiles, of eyght foote length, of moste pleasaunte taste. [Richard Eden, "Decades of the New World," 1555]
also Protorosaurus, extinct genus of lizard-like reptiles first found fossilized in rocks from the late Permian in Germany and Britain, 1872, from Latinized form of Greek proteros "former, earlier" (see protero-) + sauros "lizard" (see -saurus). So called because it was long the earliest known fossil reptile.
1580s, from French scinc (Modern French scinque), from Latin scincus, from Greek skinkos, some kind of lizard common in Asia and North Africa, of unknown origin.