define

verb

1. To determine with precision; to mark out with distinctness; to ascertain or exhibit clearly.

   “the defining power of an optical instrument”

   “Rings[…]very distinct and well defined.”

   “Turbines have been around for a long time—windmills and water wheels are early examples. The name comes from the Latin turbo, meaning vortex, and thus the defining property of a turbine is that a fluid or gas turns the blades of a rotor, which is attached to a shaft that can perform useful work.”

2. (obsolete)To settle, decide (an argument etc.)

   “These warlike Champions, all in armour shine, / Assembled were in field the chalenge to define.”

3. To express the essential nature of something.

   “I define myself as a techno-anarchist.”

   “Your past mistakes do not define who you are.”

   “Cantor defined a one-to-one correspondence between the points of the square and the points of the line segment. Every point in the square was associated with a single point in the segment; every point in the segment was matched with a unique point in the square.”

4. To state the meaning of a word, phrase, sign, or symbol.

   “The textbook defined speed as velocity divided by time.”

5. To describe, explain, or make definite and clear; used to request the listener or other person to elaborate or explain more clearly his or her intended meaning of a word or expression.

   “Person 1: Is she good at math? Person 2: Define "good." If you mean if she is faster than the average middle schooler at multiplication, then yes. If you mean if she is able to do multivariable calculus, then no.”

6. To demark sharply the outlines or limits of an area or concept.

   “to define the legal boundaries of a property”

   “Few concepts are as emotionally charged as that of race. The word conjures up a mixture of associations—culture, ethnicity, genetics, subjugation, exclusion and persecution. But is the tragic history of efforts to define groups of people by race really a matter of the misuse of science, the abuse of a valid biological concept?”

7. To establish the referent of a term or notation.

noun

1. A kind of macro in source code that replaces one text string with another wherever it occurs.

   “From the computer programming perspective, Java looks like C and C++ while discarding the overwhelming complexities of those languages, such as typedefs, defines, preprocessor, unions, pointers, and multiple inheritance.”

   “Anyone who has attempted to do OO programming in a conventional language using defines will find out that it is impossible to realize the benefits easily, if at all, without compiler support.”