resolute
stoical
solid
mettlesome
undestroyable
tenacious
foursquare
firm, strong
lasting
strong, sound, secure, solid (gloss)
(syn)
firm, steadfast, secure, solid, fast (gloss)
(coi)
firm, steadfast (gloss)
firm, hard (gloss)
loud
(ant)
fast (gloss)
(inflection of)
strong, significant
enthusiastic