refusing to give in

unyielding

determined and stubborn when trying to solve or complete something

determined, persistent

that cannot be moved; not able, refusing to be affected or changed

fixed, stubborn

implied though not openly expressed; done without questioning

included without question, inherent, absolute

that cannot be disputed

beyond dispute

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

stubborn

stubborn

pig-headed, stubborn

very determined

determined, strong-willed

not in the form of a liquid or gas; without holes or spaces; of strong material or construction; able to support weight etc

hard, dimensional

(of a person) having a strong, determined will; difficult to deal

obstinate, unyielding

having good reasons to believe something; free from doubt; proved; reliable; without a doubt

certain, definite

holding tightly; very determined to get or keep something, be successful in winning an argument etc

strong, unyielding

not afraid

fearless

that cannot be broken

strong, tough