verb

• (intransitive, originally US, often imperative) To leave in a hurry; to go away.
  "What are you kids doing on my lawn? Scram!"

noun

• (MLE, slang) A gun, firearm.
  "Bad be say she don’t usually do this In the trap with a stick, I do this Get ’round there with a scram I don’t give a damn"

verb

• (transitive) To shut down (a nuclear reactor or, by extension, some other thing) for safety reasons, usually because of an emergency.
  "The NCR [Nuclear Regulatory Commission] further demands the plant conform to all the safety requirements put into effect during construction. This means constant re-design. There must also be several ways to scram (emergency shut down) the reactor. Some of these are automatic and some are manual."
• (intransitive) Of a nuclear reactor or some other thing: to shut down, usually because of an emergency.
  "This shut off current to the control rod mechanism, and the reactor scrammed (shut off) automatically."

noun

• (also attributively) A shutdown of a nuclear reactor (or, by extension, some other thing), often done rapidly due to an emergency.
  "During scram operation, a scram signal de-energizes the inlet and outlet scram valves. The outlet scram valve vents the volume above the drive piston to a scram dump tank. The inlet scram valve supplies scram pressure obtained from an accumulator to the under side of the vented piston."