(mathematics, logic) Of one of a series of models, languages, relationship, forms of logical discourse, etc., being the simplest one or the first in a sequence. / Of fundamental importance.

A stream that has no permanent tributaries.

plural of first order stream

(logic) A formal deductive system extended from propositional logic with the possibility to quantify over individuals of the domain of discourse.

(physics) A spectrum produced by a diffraction grating whose adjacent slits are one wavelength apart.

plural of first order of the day

(politics) An item of business that will be discussed before any other item on a particular day when a legislature is sitting.

plural of first-order spectrum

plural of first-order logic