| necessary(adjective, essential, required, obligatory, needed) |
| all-important(adjective, significant, essential, basic, vital) |
| binding(adjective, significant, essential, basic, vital) |
| bottom-line(adjective, significant, essential, basic, vital) |
| chief(adjective, significant, essential, basic, vital) |
| compelling(adjective, significant, essential, basic, vital) |
| compulsory(adjective, significant, essential, basic, vital) |
| de rigueur(expression, adjective, significant, essential, basic) |
| decisive(adjective, significant, essential, basic, vital) |
| dutiful(adjective, obedient, well-behaved) |
| exigent(adjective, significant, essential, basic, vital) |
| expedient(adjective, significant, essential, basic, vital) |
| fundamental(adjective, significant, essential, basic, vital) |
| imperative(adjective, significant, essential, basic, vital) |
| incumbent |
| mandatory(adjective, significant, essential, basic, vital) |
| momentous(adjective, significant, essential, basic, vital) |
| name of game(expression, adjective, idiom, significant, essential) |
| needed(adjective, significant, essential, basic, vital) |
| needful(adjective, significant, essential, basic, vital) |