| basis(noun, idea, base, foundation) |
| foundation(noun, hold, block, back) |
| principle(noun, idea, foundation, essence) |
| sine qua non(noun, expression, idiom, foundation) |
| heart(noun, idea, foundation, essence) |
| rudiment(noun, base, foundation, basic) |
| axiom(noun, foundation, basic, stipulation) |
| element(noun, foundation, basic, stipulation) |
| bottom line(noun, expression, foundation, basic) |
| rock bottom(expression, foundation, basic, stipulation) |
| rule(noun, foundation, basic, stipulation) |
| ABCs(base, foundation, basic, basis) |
| basic(foundation, stipulation, tenet, axiom) |
| brass tacks(noun, expression, foundation, basic) |
| coal and ice(noun, expression, idiom, foundation) |
| constituent(foundation, basic, stipulation, tenet) |
| essential part(noun, expression, foundation, basic) |
| factor(foundation, basic, stipulation, tenet) |
| guts(foundation, basic, stipulation, tenet) |
| nitty-gritty(foundation, basic, stipulation, tenet) |