solid and firm; not easy to bend, dent, cut etc

rocklike

that cannot be bent; refusing to change or be influenced

stubborn

the commonest metal (symbol Fe), used in manufacturing and building, an also forming an essential part of blood; a flat-bottomed implement heated and used for smoothing clothes etc

hard, tough; inflexible

an animal that is the young of a horse and a donkey; a slipper without a heel

stubborn

stiff; that cannot be bent; firm; strict; not changing

stiff, strict, severe

that cannot be broken

strong, tough