My prefix gets the guns.
My infix makes things dull.
My suffix appears at zero.
My whole indicates a lull.
What am I?
You are:
an Armistice
My prefix gets the guns.
Arm: as in 'to get weapons'
My infix makes things dull.
Mist: makes thing dreary and can erode
My suffix appears at zero.
Ice: appears at 0 degrees Celsius
My whole indicates a lull.
Armistice: an agreement in a war to stop fighting for a certain time; ie, a lull