adj. 1a. being or relating to the first derivative of a function.
b. in particular, (of an ordinary differential equation) involving the first derivative, but no higher order differential coefficients, of the dependent variable with respect to the independent variable.
c. (of a partial differential equation) involving no partial differential coefficient of order greater than 1. 2. (Logic) quantifying only over individuals and not over predicates or classes. Lower or first order predicate calculus (LPC) studies the logical properties of such quantification. Compare second-order. 3. see tensor. 4. also of the first order. having unit order. Compare second-order.