I guess that I have a general definition of toughness that fits for most aspects:
Toughness is when you intentionally withstand discomfort, inconvenience, or emotional upheaval in the pursuit of something larger than the right now.
In most real life cases, toughness is really about deferring gratification, or accepting current hardship on behalf of something worth having....in the case of someone very sick, it is the hope that one day they will get better. In the case of someone that came from nothing to grow into being successful, it was the belief that one day their work, their sacrifice, would pay off. In the case of a guy deciding to deadlift 450 instead of an hour on an elliptical, it is the belief that it will make them stronger, look better naked, etc....the point is that there is a common thread.
I have told people how some of the toughest people I have ever met were in med school....the stereotype that they are legacy kids is exactly that, and a false one. Some of them had grown up very poor, were not really the most intelligent people one would ever meet, but HOLY hell were they relentless. I always say that when I think of doctors, I don't think "smart", I think "tough". For them, it was their way of saying that they made it out, that they had made something of themselves no one could argue with. A lot of academic pursuits do this for people, and it doesn't get as much credit as it should....the toughest person I ever met went from being essentially homeless to having a computer engineering degree from Purdue. He was unshakable with everything he did. It spills over into everything.
For my people, tt was 6+ years of often 16-18 hour days, no such thing as a weekend, usually with finals right after the holidays. Saturday night meant you simply got to study a little later than normal. No sleep, bad food, and it just never ends. No breaks, no "taking a long weekend", often not a single night off for months on end.
I remember having a calender that I got as a Christmas gift one year....I took New Years off, and was about to head into the toughest semester we had (2nd of 2nd year). I wrote across the whole calender, with a Sharpie, until May when finals came: "Every day is war"
Now it all feels like a million years ago with my life now. I at least had the luxury of getting my mettle truly tested. I am fortunate enough for that. It does something to you....
A friend of mine had a song lyric that she would write on the top of her final's study guides that I still remember. It said: "I swim for brighter days, despite the absence of sun." That is toughness for me, in many of its forms.
"They now look to a single and splendid government of an aristocracy, founded on banking institutions, and moneyed incorporations under the guise and cloak of their favored branches of manufactures, commerce and navigation, riding and ruling over the plundered ploughman and beggared yeomanry." - Thomas Jefferson, 1826