1.
If someone is in the ~ of something such as a revolution or an area of research, they are involved in the most advanced part of it. You can also refer to the people themselves as the ~.
Such thinking puts Kodak in the ~ of a movement reshaping the computer industry...
...the role of the Party as the political ~.
N-SING: usu the N, oft in the N of n
2.
The ~ of an army is the part of it that goes into battle first.
...a force of mobile reserve units that could strike quickly and effectively at the ~ of an invading army.
N-SING: the N