double-action 
adjective
1Combining two different functions; double-acting: double-action moss killer...
- A new, double-action vaccine that protects children against diphtheria and whooping cough at the same time was described at the Atlantic City meeting of the American Public Health Association last week.
- It was now precision built of hollow aluminum tubing and boasted an adjustable, double-action spring.
2(Of a gun) able to be cocked and fired in one single action.A double-action revolver can be fired in a matter of seconds by anyone strong enough to pull a trigger, including the bad guy or a five-year-old child....
- In handguns, the double-action revolver has traditionally been the recommendation of those who believe in the KISS principle: Keep It Simple, Stupid.
- This was in no small part due to the fact Walther offered double-action pistols long before any American gun company did.