leaf

Etymology

From Middle English leef, from Old English lēaf, from Proto-West Germanic *laub, from Proto-Germanic *laubą (“leaf”), from Proto-Indo-European *lowbʰ-o-m, from *lewbʰ- (“leaf, rind”) See also West Frisian leaf, Low German Loov, Dutch loof, German Laub, Danish løv, Swedish löv, Norwegian Nynorsk lauv, Icelandic lauf; also Irish luibh (“herb”), Latin liber (“bast; book”), Lithuanian lúoba (“bark”), Albanian labë (“rind”), Latvian luba (“plank, board”), Russian луб (lub, “bast”). (Internet slang: Canadian): In reference to the maple leaf as national symbol.

noun

1. The usually green and flat organ that represents the most prominent feature of most vegetative plants.
   Earless ghost swift moths become “invisible” to echolocating bats by forming mating clusters close (less than half a meter) above vegetation and effectively blending into the clutter of echoes that the bat receives from the leaves and stems around them. 2013 May-June, William E. Conner, “An Acoustic Arms Race”, in American Scientist, volume 101, number 3, pages 206–7
2. Anything resembling the leaf of a plant.
3. A sheet of a book, magazine, etc (consisting of two pages, one on each face of the leaf).
4. A sheet of any substance beaten or rolled until very thin.
   gold leaf
5. (advertising, dated) Two pages.
   Heretofore advertisers have had to buy and pay for a leaf — two pages. 1900, Profitable Advertising, volume 10, number 2, page 893
6. (in the plural) Tea leaves.
7. A flat section used to extend the size of a table.
8. (plural leaves or leafs) A moveable panel, e.g. of a bridge or door, originally one that hinged but now also applied to other forms of movement.
   Meronym: stile
   The train car has one single-leaf and two double-leaf doors per side.
   The bridge shear locks were repaired and the long ends of the shear locks shortened about two inches to eliminate butting of the bridge leafs against each other. 1914, Department of Bridges, City of New York, Report, page 90
   It will be noted that the pivotal mounting of the cylinders is such that the cylinders have their greatest leverage (i.e., exert the greatest door-opening force) when the door leafs 24, 28 are closed because the cylinders are generally perpendicular to the closed leafs. This is desirable because the load on the leafs is the greatest when they are closed due to air pressure. As the leafs begin to open and this air pressure decreases, the opening force exerted by the cylinders on the door leafs decreases and the opening speed of the leafs increases. 21 July 1992, William R. Kennedy, John M. Kennedy, Power mine door system, US Patent 5,222,838
   THE NTSB RECOMMENDS THAT THE U.S. COAST GUARD: REQUIRE OWNERS/OPERATORS OF BASCULE BRIDGES TO INSTALL CAUTION LIGHTS AND DAYLIGHT MARKINGS AT ELEVATION POINTS ON BRIDGE LEAFS WHERE THEY PROTRUDE OVER NAVIGABLE CHANNELS TO IDEN TIFY TO MARINERS THE POINT AT WHICH FULL SKYWARD CHANNEL CLEARANCE IS NOT AVAILABLE TO TRANSITING VESSELS: THE LIGHTS SHOULD ACTIVATE WHEN THE BRIDGELEAFS ARE IN THE NORMAL FULLY OPEN POSITION.[…]THE NTSB RECOMMENDS THAT THE U.S. COAST GUARD: REQUIRE THAT BRIDGE OWNERS/OPERATORS PROVIDE IN BASCULE BRIDGE PERMIT APPLICATIONS THE ANGLE OF THE BRIDGELEAF(S). THE MAXIMUM VERTICAL CLEARANCE AT THE FENDERS AND AT THE BRIDGELEAF ENDS, AND THE EXTENT OF HORIZONTAL CHANNEL CLEARANCE OVER WHICH FULL SKYWARD CLEARANCE IS AVAILABLE WHEN THE BRIDGE LEAFS ARE IN THE FULLY OPEN POSITION. 1993, Department of Transportation and Related Agencies Appropriations for 1994: Hearings Before a Subcommittee of the Committee on Appropriations, House of Representatives, One Hundred Third Congress, First Session, Washington, D.C.: U.S. Government Printing Office, page 136
   The four separate segments of the movable bridge span, known as bridge leafs, were alternately rehabilitated while maintaining upper-level roadway and pedestrian traffic on one-half of the bridge and waterway traffic on one-half of the river channel. 1993, Realty and Building, page 20
   The hydraulic system lifts and rotates two 413-ft (126-m) bridge leafs, each weighing 7,500 tons, in just four minutes. 1993, The Americana Annual: An Encyclopedia of Current Events, Grolier, →ISSN, →LCCN, page 224
   Note the Art Deco-style sculptures on the wall of the bridge house showing a ship passing under the raised bridge leafs. 1996, Gerard R. Wolfe, Chicago in and Around the Loop: Walking Tours of Architecture and History, McGraw-Hill, page 150
   Like I’ve said, John, you’ve got to get the two bridge leafs to come down very slowly to a complete stop in order to trigger the tongue locks. This is what holds the two leafs of the bridge firmly in place. Otherwise, the bridge leafs will start bouncing, and once they start bouncing, you’ll never stop them from goin’ straight up in the air. 2010, James Newport-Chiakulas, Bridges to Justice: Love, Murder, & Politics in Chicago, iUniverse, page 55
9. (botany) A foliage leaf or any of the many and often considerably different structures it can specialise into.
10. (computing, mathematics) In a tree, a node that has no descendants.
    The algorithm pops the stack to obtain a new current node when there are no more children (when it reaches a leaf). 2011, John Mongan, Noah Kindler, Eric Giguère, Programming Interviews Exposed
11. The layer of fat supporting the kidneys of a pig, leaf fat.
12. One of the teeth of a pinion, especially when small.
13. (slang, uncountable) Cannabis.
14. (Internet slang, humorous, sometimes pejorative, plural leafs) A Canadian person.

verb

1. (intransitive) To produce leaves; put forth foliage.
2. (transitive) To divide (a vegetable) into separate leaves.
   The lettuce in our burgers is 100% hand-leafed.