| TANGENT | The ratio of sine to cosine |
| SECANT | In trigonometry, the ratio of the hypotenuse of a right-angled triangle to that of the adjacent side; the reciprocal of the cosine (6) |
| NEPER | Unit used in physics to express the ratio of two quantities, equal to the natural logarithm of the ratio of the quantities (5) |
| MACH | Physicist who established the principles of supersonics and the ratio of the velocity of a body to the speed of sound (4) |
| SINE | In a right-angled triangle, the ratio of the length of the side opposite an angle to the length of the hypotenuse (4) |
| COSECANT | In geometry, the ratio of the length of the hypotenuse in a right-angled triangle to that of the opposite side (8) |
| EFFICIENCY | A measure of a mechanical system's effectiveness, usually the ratio of the power delivered by a mechanical system to the power supplied to it (10) |
| MACHNUMBER | Parameter designated to the ratio of an aircraft's velocity divided by the speed of sound at that altitude (4,6) |
| MPH | The ratio of the distance traveled (in miles) to the time spent traveling (in hours). |
| DENSITY | The ratio of the mass of a substance to its volume (7) |
| RATEOFRETURN | The ratio of the annual income from an investment to the original investment, often expressed as a percentage (4,2,6) |
| COTANGENTREASON | Basis for using the ratio of adjacent and opposite sides of a triangle, relative to an angle? |
| DETRIMENT | In physics, the ratio of the amplitudes in successive cycles of a damped oscillator (9) |
| UMBILICALACCORD | Agreement on the ratio of innies to outies? |
| BIRTHRATE | The ratio of live births per thousand of population per year (5,4) |
| PI | The ratio of a circle's circumference to its diameter (2) |
| EULER | Mathematician who popularized pi to denote the ratio of a circle |
| GAIN | Factor by which power or voltage is increased by an amplifier, expressed as the ratio of output to input (4) |
| FRACTION | Any rational number that can be expressed as the ratio of two integers (8) |
| COSEC | (In mathematics) the reciprocal of sine (abbr) (5) |
