Adjective
(idiomatic, simile) Having a hard, strong, and determined mindset.
(simile) Very hard; tough
Source: en.wiktionary.orgMom spent the time that she was supposed to be a kid actully raising children, her younger brother and younger sister. She was tough as nails and did not suffer fools at all. And the truth was she could not afford to. She spoke the truth, bluntly, directly, and without much varnish. I am her son. Chris Christie
My granddad was an evangelist, and my grandma, she was as tough as nails. She watched 'American Bandstand' every day when she was in her 80s, 90s. She loved rock music. I never had anyone in my family that was anti-rock n' roll. Alice Cooper
We found that the most exciting environments, that treated people very well, are also tough as nails. There is no bureaucratic mumbo-jumbo... excellent companies provide two things simultaneously: tough environments and very supportive environments. Tom Peters
I just try to stay positive and focused on the tennis, not let anything get to me, like crazy questions. But I'm tough, let me tell you, tough as nails. Venus Williams