| uncompassionate(adjective, mean, hard, tough, harsh) |
| uncooperative(adjective, mean, hard, tough, difficult) |
| undeviating |
| unfading(adjective, stable, constant, vast, enduring) |
| unflappable(adjective, firm, solid, determined, usual) |
| unflexible(adjective, tough, firm, fixed, stiff) |
| unfluctuating(adjective, calm, strong, secure, firm) |
| uniform(adjective, calm, strong, secure, firm) |
| unimpressible(adjective, mean, hard, tough, harsh) |
| united(adjective, complete, steady, stable, jellied) |
| unsympathetic(adjective, mean, hard, tough, harsh) |
| unvarying(adjective, calm, strong, secure, firm) |
| uptight(adjective, tough, firm, fixed, distant) |
| usual(adjective, firm, determined, regular, planned) |
| well-built(adjective, calm, strong, solid, steady) |
| well-founded(adjective, calm, strong, solid, steady) |
| well-set(adjective, firm, determined, usual, regular) |
| allegiant(adjective, firm, solid, stable, fixed) |
| ardent(adjective, firm, solid, stable, fixed) |
| arthritic |