In art, primary colors are the ones that cannot be achieved by mixing pigments – and by mixing which we get all the other colors, called complementary, secondary, and tertiary. Physics uses the term differently.
In a measuring system, base units are the fundamental units of mass, length, time, or electric current.
Unlike complex concepts (which aren't necessarily complicated), basic concepts are the ones that often (or always) defy definition and are exhausted by pointing out their examples.
To answer the question, "What is physics?" the easiest honest answer would be to point to one of the great physical theories (such as Newton's laws, Maxwell's field theory, Einstein's relativity, or quantum mechanics).
Pointing at a democratic society would be the best way to answer the question, "What is a democratic society?"
Naturally, the list of definition-defying concepts would include the three major ones: love, hope, and faith.
According to some experts, boredom is defined in Ecclesiastes as "vexation of spirit." Very well. But what is vexation of spirit? Please don't say "boredom."
What is a number? It is not a numeral: a numeral is a drawn symbol denoting a number. What is a number?
And so forth.
Is there a term for these ... basic ... elementary ... base ... rudimentary ... primary ... fundamental ... primordial ... concepts?
