fold

fold¹

—foldable, adj.

/fohld/, v.t.

1. to bend (cloth, paper, etc.) over upon itself.

2. to bring into a compact form by bending and laying parts together (often fol. by up): to fold up a map; to fold one's legs under oneself.

3. to bring (the arms, hands, etc.) together in an intertwined or crossed manner; clasp; cross: He folded his arms on his chest.

4. to bend or wind (usually fol. by about, round, etc.): to fold one's arms about a person's neck.

5. to bring (the wings) close to the body, as a bird on alighting.

6. to enclose; wrap; envelop: to fold something in paper.

7. to embrace or clasp; enfold: to fold someone in one's arms.

8. Cards. to place (one's cards) facedown so as to withdraw from the play.

9. Informal. to bring to an end; close up: The owner decided to fold the business and retire.

v.i.

10. to be folded or be capable of folding: The doors fold back.

11. Cards. to place one's cards facedown so as to withdraw from the play.

12. Informal. to fail in business; be forced to close: The newspaper folded after 76 years.

13. Informal. to yield or give in: Dad folded and said we could go after all.

14. fold in, Cookery. to mix in or add (an ingredient) by gently turning one part over another: Fold in the egg whites.

15. fold up, Informal.

a. to break down; collapse: He folded up when the prosecutor discredited his story.

b. to fail, esp. to go out of business.

n.

16. a part that is folded; pleat; layer: folds of cloth.

17. a crease made by folding: He cut the paper along the fold.

18. a hollow made by folding: to carry something in the fold of one's dress.

19. a hollow place in undulating ground: a fold of the mountains.

20. Geol. a portion of strata that is folded or bent, as an anticline or syncline, or that connects two horizontal or parallel portions of strata of different levels (as a monocline).

21. Journalism.

a. the line formed along the horizontal center of a standard-sized newspaper when it is folded after printing.

b. a rough-and-ready dividing line, esp. on the front page and other principal pages, between stories of primary and lesser importance.

22. a coil of a serpent, string, etc.

23. the act of folding or doubling over.

24. Anat. a margin or ridge formed by the folding of a membrane or other flat body part; plica.

[bef. 900; (v.) ME folden, falden, OE faldan; c. G. falten; (v.) ME fald, deriv. of the n.; akin to L plicare to fold, plectere to PLAIT, twine, Gk plékein; cf. -FOLD]

fold²

/fohld/, n.

1. an enclosure for sheep or, occasionally, other domestic animals.

2. the sheep kept within it.

3. a flock of sheep.

4. a church.

5. the members of a church; congregation: He preached to the fold.

6. a group sharing common beliefs, values, etc.: He rejoined the fold after his youthful escapade.

v.t.

7. to confine (sheep or other domestic animals) in a fold.

[bef. 900; ME fold, fald, OE fald, falod; akin to OS faled pen, enclosure, MLG valt pen, enclosure, manure heap, MD vaelt, vaelde]

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In geology, an undulation or wave in the stratified rocks of the Earth's crust.

Stratified rocks were originally formed from sediments that were deposited in flat, horizontal sheets, although in some places the strata are no longer horizontal but have warped. The warping may be so gentle that the inclination of the strata is barely perceptible, or it may be so pronounced that the strata of the two flanks are essentially parallel or nearly flat. Folds vary widely in size; the tops of large folds are commonly eroded away on the Earth's surface.

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▪ geology

      in geology, undulation or waves in the stratified rocks of the Earth's crust. Stratified rocks were originally formed from sediments that were deposited in flat, horizontal sheets, but in a number of places the strata are no longer horizontal but have been warped. Sometimes the warping is so gentle that the inclination of the strata is barely perceptible, or the warping may be so pronounced that the strata of the two flanks may be essentially parallel or lie nearly flat (as in the case of a recumbent fold). Folds vary widely in size; some are several kilometres or even hundreds of kilometres across, and others measure just a few centimetres or less. The tops of large folds are commonly eroded away on the Earth's surface, exposing the cross sections of the inclined strata.

  Folds are generally classified according to the attitude of their axes and their appearance in cross sections perpendicular to the trend of the fold. As shown in Figure 1—>, the axial plane of a fold is the plane or surface that divides the fold as symmetrically as possible. The axial plane may be vertical, horizontal, or inclined at any intermediate angle, as in the folds in Figure 2—>. An axis of a fold is the intersection of the axial plane with one of the strata of which the fold is composed.

      Although in the simpler types of folds the axis is horizontal or gently inclined, it may be steeply inclined or even vertical. The angle of inclination of the axis, as measured from the horizontal, is called the plunge. The portions of the fold between adjacent axes form the flanks, limbs, or slopes of a fold.

     An anticline is a fold that is convex upward, and a syncline is a fold that is concave upward (Figure 2—>). An anticlinorium is a large anticline on which minor folds are superimposed, and a synclinorium is a large syncline on which minor folds are superimposed. A symmetrical fold (Figure 2—>) is one in which the axial plane is vertical. An asymmetrical fold (Figure 2—>) is one in which the axial plane is inclined. An overturned fold, or overfold, has the axial plane inclined to such an extent that the strata on one limb are overturned (Figure 2—>). A recumbent fold has an essentially horizontal axial plane (Figure 2—>). When the two limbs of a fold are essentially parallel to each other and thus approximately parallel to the axial plane, the fold is called isoclinal.

      Many folds are distinctly linear; that is, their extent parallel to the axis is many times their width. Some folds, however, are not linear but are more or less circular in plan. A dome is such a fold that is convex upward; this means that its strata dip outward from a central area. A basin (tectonic basins and rift valleys) is a circular fold that is concave upward—i.e., the strata dip inward toward a central area.

      The long linear folds that are characteristic of mountainous regions are believed to have resulted from compressional forces acting parallel to the surface of the Earth and at right angles to the fold. Some geologists believe that many folds are the result of strata sliding from a vertically uplifted area under the influence of gravity. The push exerted by an advancing glacier also may throw weakly consolidated rocks into folds, and the compaction of sedimentary rocks over buried hills gives rise to gentle folds. In nature, folds are rarely produced by a single process but by a combination of processes.

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