met ‧ tle /ˈmetl/ BrE AmE noun [uncountable]
[ Date: 1500-1600 ; Origin: metal ]
1 . courage and determination to do something even when it is very difficult
test/show/prove your mettle
a crisis which will test the minister’s mettle
2 . on your mettle British English if you are on your mettle, you are ready to try as hard as possible because your abilities are being tested:
We’ll have to be on our mettle from the start.
keep/put somebody on their mettle
This was just his way of keeping me on my mettle.