stiffer, harder, stricter, harsher, tighter, toughened, sterner, easier, rougher, stronger, trickier, better, fiercer, friendlier, difficult, looser, stringent, bigger, softer, worse, nastier, steeper, sharper, quicker, bumpier, bolder, clearer, weaker, uglier, kinder, meaner, hungrier, daunting, smarter, laxer, challenging, heavier, braver, crueler, feistier, crazier, calmer, scarier, hotter, stingier, simpler, nicer, dicey, shakier, lenient, sweeter, gutsier, heftier, angrier, murkier, rockier, swifter, grimmer, sorer, aggressive, stickier, testier, busier, rough sledding, tenser, gloomier, prettier, gentler, onerous, cloudier, milder, fewer, fresher, hairier, warier, speedier, livelier, messier, rosier, louder, firmer, greater, riskier, mandatory, dirtier, shorter, beefier, faster, slower, thornier, lighter, shrewder, safer, chillier, quieter, healthier, wilder, fairer, cheaper, cozier, cleverer, smoother, tough, toughest, draconian, hardest, demanding, stiffest, lax, easiest, antitrust

cold rubber, powerfully, redoubtable, toughen