also cloverleaf, "the leaf of a clover plant," 1787, from clover + leaf (n.). Highway interchange sense attested by 1933, so called for the shape.
Entries linking to clover-leaf
clover n.
plant of the genus Trifolium, widely cultivated as fodder, Middle English claver, from Old English clafre, clæfre "clover," from Proto-Germanic *klaibron (source also of Old Saxon kle, Middle Low German klever, Middle Dutch claver, Dutch klaver, Old High German kleo, German Klee "clover"), which is of uncertain origin. Klein and Liberman write that it is probably from West Germanic *klaiwaz- "sticky pap" (see clay), and Liberman adds, "The sticky juice of clover was the base of the most popular sort of honey."
The modern spelling prevailed after c. 1700. The exact phrase four-leafed clover attested from 1831; first reference in English to the supposed luck of a four-leaf clover is from c. 1500 ("The Gospelles of Dystaues"). The ratio of four- to three-leaved clovers is said to be 1 in 10,000 or 1 in 5,000. To be in clover "live luxuriously" is 1710, "clover being extremely delicious and fattening to cattle" [Johnson].
leaf n.
Old English leaf "leaf of a plant, foliage; page of a book, sheet of paper," from Proto-Germanic *lauba- (source also of Old Saxon lof, Old Norse lauf, Old Frisian laf, Dutch loof, Old High German loub, German Laub "foliage, leaves," Gothic laufs "leaf, foliage"), perhaps from PIE *leub(h)- "to peel off, strip or break off" ((source also of Old Irish luib, "herb," lub-gort "garden;" Albanian labë "rind, cork;" Lithuanian luba "plank, board;" Russian lob "forehead, brow," Czech leb "skull;" Lithuanian luobas "bast," Latvian luobas "peel," Russian lub "bast;" Old Norse lyf "medicinal herbs," Old English lybb "poison; magic").
Related to lodge and lobby; for another PIE root see folio. Extended late 14c. to very thin sheets of metal (especially gold). Compare Lithuanian lapas "leaf," from a root also in Greek lepos "bark," lepein "to peel off." Also applied to flat and relatively broad surfaces, especially of flexible or mounted attachments; meaning "hinged flap on the side of a table" is from 1550s. To turn over a (new) leaf (1590s; 1570s as turn the leaf) "begin a new and better course of life" is a reference to the book sense. Among insects, leaf-hopper is from 1847; leaf-cutter from 1816.