| demanding(tough, severe, important, serious, painful) |
| difficile(tough, severe, painful, problematic, trying) |
| difficult(adjective, hard, tough, severe, problematic) |
| earnest(big, heavy, significant, substantial, valuable) |
| earth-shaking(adjective, important, significant, serious, critical) |
| earth-shattering(important, significant, serious, critical, historic) |
| earthshaking(adjective, important) |
| easier said than done(expression, tough, severe, painful, problematic) |
| effortful(tough, severe, painful, problematic, trying) |
| embryonic |
| emergent |
| enduring(great, extraordinary, outstanding, notable, unforgettable) |
| epoch-making |
| exacting(tough, severe, important, serious, painful) |
| extraordinary(great, outstanding, notable, unforgettable) |
| extreme(adjective, intense, last, impulsive, final) |
| far-reaching(severe, big, important, significant, substantial) |
| fat(big, heavy, substantial) |
| first(adjective, important, significant, original, basic) |
| focal(adjective, key, chief, principal, foremost) |