master key 
noun
A key that opens several locks, each of which also has its own key: the master key for all the safes in the department...
- The change key will open only that specific lock, while the master key will open that lock and several others in a group.
- She used her master key to open the lock, and began to open the gate.
- I got the master key and opened the door and that's when I saw him in the bath.
- repetition choice
- repetition clock
- repetition compound
- repetition compulsion
- repetition device
- repetitionist
- repetition phenomenon
- repetition running
- repetition sermon
- repetition training
- repetition work
- repetitious
- repetitiously
- repetitiousness
- repetitive
- forget-me-not
- forgettable
- forgetter
- forgivable
- forgivably
- forgive
- forgiveness
- forgiver
- forgiving
- forgivingly