WordNet sense 1 (able to withstand attack):

impregnable, inviolable, secure, unassailable, unattackable

WordNet sense 2 (characterized by energy and vigor):

virile

WordNet sense 3 (characterized by great force or energy):

vehement

WordNet sense 4 (powerful):

stiff

WordNet sense 5 (strong enough to withstand or overcome intellectual challenges or adversity):

robust

WordNet sense 6 (strong enough to knock down or overwhelm):

powerful

WordNet sense 7 (very strong or vigorous):

hard, knockout, severe

WordNet sense 8 ((of a person) possessing physical strength and weight; rugged and powerful):

brawny, muscular, sinewy

WordNet sense 9 (of good quality and condition; solidly built):

solid, substantial

WordNet sense 10 (in good condition; free from defect or damage or decay):

sound

WordNet sense 11 (contrary to rule or accepted order or general practice):

irregular

WordNet sense 12 (having or wielding force or authority):

potent

WordNet sense 13 (in an extreme degree):

intense

WordNet sense 14 (freshly made or left):

warm

WordNet sense 15 (recently made, produced, or harvested):

fresh

WordNet sense 16 (strong and sure):

firm

WordNet sense 17 (characterized by or full of force or strength (often but not necessarily physical)):

forceful