Strong
robust, wiry, mighty; see strong 1, 2.
Cohesive
solid, firm, sturdy, hard, hardened, adhesive, leathery, coherent, inseparable, molded, tight, cemented, unbreakable, in one piece, dense, closely packed.
Antonyms weak*, fragile, brittle.
Difficult to chew
uncooked, half-cooked, gristly, sinewy, indigestible, inedible, fibrous, old, tough as shoe-leather*; see also raw 1.
Antonyms soft*, tender, overcooked.
Difficult
unyielding, hard, resisting, troublesome, onerous, intricate, puzzling, laborious; see also difficult 1, severe 1.
Antonyms easy*, simple, obvious.
Hardy
robust, sound, capable; see healthy 1.
*Rough and cruel
savage, fierce, desperate, ferocious, ruffianly, uproarious, terrible, rapacious, riotous, uncontrollable, unmanageable.
Antonyms friendly*, genial, easygoing.
*Unfavorable
bad, unfortunate, untimely; see unfavorable 2.
*Excellent
fine, first-class, premium; see excellent.