Possible Clues:

• Trig function used to model light waves
• Function yielding 0 when applied to pi
• Ratio of an angle's opposite side to the hypotenuse
• Function for mathematicians at home in the home counties
• Homophone of 'sign'
• Bad European function
• What the S of “sohcahtoa” stands for
• 0, for 0°
• The "S" in trig's SOHCAHTOA
• Math term from the Latin for “curve”