WordNet sense 1 (having rugged physical strength; inured to fatigue or hardships):

hardy, stalwart, stout

WordNet sense 2 (physically strong):

robust

WordNet sense 3 (not making concessions):

inflexible, uncompromising

WordNet sense 4 (substantially made or constructed):

tough

WordNet sense 5 (sturdy and strong in constitution or construction; enduring):

rugged, rugged