Noun

1. A piece or lock of curling hair; a ringlet.
   • 1866, Louisa May Alcott, Behind A Mask or, A Woman's Power, chapter 7:

     she took it down, looked long and fondly at it, then, shaking her curls about her face, as if to hide the act, pressed it to her lips and seemed to weep over it in an uncontrollable paroxysm of tender grief.

2. A curved stroke or shape.
   • 1995, John Curtis, Julian Reade, & Dominique Collon, Art and Empire: Treasures from Assyria in the British Museum‎, page 184:

     the backs of their necks and their forelegs are decorated with curls and their necks and bodies are covered with fine, undulating lines.

3. A spin making the trajectory of an object curve.
   • 1909, Harold Horsfall Hilton, The Six Handicap Golfer's Companion^{http://books.google.com/books?id=fZ0XAAAAYAAJ}, page 38:

     It is possible to use the wind which blows from the left to the right by playing well into the wind with the slightest bit of curl on the ball

4. Movement of a moving rock away from a straight line.
5. Any exercise performed by bending the arm, wrist, or leg on the exertion against resistance, especially those that train the biceps.
   • 2007 (Jan/Feb), Jon Crosby, "Your Winter Muscle Makeover", Men's Health, page 54:

     Now do a curl and an overhead press, keeping your palms facing in.

6. The vector field denoting the rotationality of a given vector field.

   The curl of the vector field $\backslash vec\{F\}=(xyz,xyz,xyz)$ is the vector field $\backslash vec\{\backslash nabla\}\backslash times\backslash vec\{F\}=(xz-xy,xy-yz,yz-xz)$.

   • 1995, Erich Prisner, Graph dynamics:

     In 2D, when Q is a polygonal domain, the singularities of Type (2) disappear because ψ is the scalar curl of u and is such that its vectorial curl is zero.

7. The vector operator, denoted $\backslash rm\{curl\}\backslash ;$ or $\backslash vec\{\backslash nabla\}\backslash times\backslash vec\{\backslash left(\backslash cdot\backslash right)\}$, that generates this field.
8. Any of various diseases of plants causing the leaves or shoots to curl up; often specifically the potato curl.
   • 1840, "Farmers' Department", The Family Magazine, volume 1, page 227:

     These potatoes, however, planted the next year, have a fair yield, untouched by the curl.

Verb

1. To cause to move in a curve.
   • 1998, Nick Hornby, Fever Pitch‎, page 70

     He picked the ball up about forty yards out on the left wing, left a trail of Arsenal defenders in his wake, and curled the ball round Geoff Barnett as he came right out into the far corner.

2. To make into a curl or spiral.
   • 2004, Jacquelyn Mitchard, Twelve Times Blessed‎, page 249

     She curls her spine; she wedges a pillow between her knees.

3. To assume the shape of a curl or spiral.
   • 1847, Charlotte Brontë, Jane Eyre‎, chapter XXXI

     It seemed to me that Mr. St. John's under lip protruded, and his upper lip curled a moment.

4. To move in curves.
   • 1977, Scott O'Dell, Carlota‎, page 1

     Clouds curled down from the mountains.

   • 2007, John Coyne, The Caddie Who Knew Ben Hogan‎, page 97

     The ball curled to a stop within six inches of the hole.

5. To take part in the sport of curling

   I curl at my local club every weekend.

6. To exercise by bending the arm, wrist, or leg on the exertion against resistance, especially of the biceps.
   • 2008, Joseph Lee Klapper, The Complete Idiot's Guide to Boosting Your Metabolism‎, page 119

     When curling the weight, bring the barbell up toward the chin, then return it to its starting position. Keep your elbows and upper arms as immobile as possible to isolate the biceps.