also front-line
(~s)
1.
The ~ is the place where two opposing armies are facing each other and where fighting is going on.
...a massive concentration of soldiers on the ~.
N-COUNT: usu the N
2.
A ~ state shares a border with a country that it is at war with or is in conflict with.
...the front-line states bordering South Africa.
ADJ: ADJ n
3.
Someone who is in the ~ has to play a very important part in defending or achieving something.
Information officers are in the ~ of putting across government policies.
PHRASE: v-link PHR, PHR after v