fer·reus^[1]

cruel
hard
made of iron
unbending
unfeeliing

Synonyms for ferreus

atrox – cruel, harsh, horrible, terrible
crudelis – cruel
difficilis – difficult, hard, troublesome
durus – enduring, hard, harsh, rough, rude, strong, tough, uncouth
edurus – hard
industrius – assiduous, diligent, hard, industrious
inflexibilis – unbending
inhumanus – barbarous, cruel, inhuman, savage, uncivil, uncivilized

Similar to ferreus

ferme – about, almost
ferramenta – or shod with iron, tools made of iron
ferramentum – iron implement
ferrarius – a blacksmith, iron mines, of iron
ferrati – cuirassiers
ferratilis – in chains
ferratus – a soldier in armor, furnished with iron, in chains, iron
ferrugineus – dusky, rust colored
ferrugo – the color of rust
ferrum – arms, horseshoe, iron, sword