differential (ˌdɪfəˈrɛnʃəl) 

—adj 
1.  of, relating to, or using a difference 
2.  constituting a difference; distinguishing 
3.  maths of, containing, or involving one or more derivatives or differentials 
4.  physics, engineering relating to, operating on, or based on the difference between two effects, motions, forces, etc: differential amplifier 

—n 
5.  a factor that differentiates between two comparable things 
6.  maths 
 a. an increment in a given function, expressed as the product of the derivative of that function and the corresponding increment in the independent variable 
 b. an increment in a given function of two or more variables, f(x_{1}, x_{2}, …x_{n}), expressed as the sum of the products of each partial derivative and the increment in the corresponding variable 
7.  See also differential gear an epicyclic gear train that permits two shafts to rotate at different speeds while being driven by a third shaft 
8.  chiefly (Brit) the difference between rates of pay for different types of labour, esp when forming a pay structure within an industry 
9.  (in commerce) a difference in rates, esp between comparable labour services or transportation routes 

differ'entially 

—adv 