All-out means using every resource available. An all-out effort.
It leaves nothing in reserve, which is why it cannot be sustained for long. An all-out attack is a decision that cannot be taken back once it has begun.
1adjectiveall-outUsing every resource available.
“They made an all-out attempt in the last twenty minutes.”
all-out is a quality.
All plus out; the phrase comes from the idea of everything being brought out at once.
From all + out.
Etymology from Wiktionary, CC BY-SA