Noun
key that secures entrance everywhere
Source: WordNetLove is the master key that opens the gates of happiness. Oliver Wendell Holmes Jr.
The balance you have between drive and patience may be your master key to success. David Allen (author)
Spirituality is indeed the master key of the Indian mind; the sense of the infinite is native to it. Sri Aurobindo
... one can still say that quantum mechanics is the key to understanding magnetism. When one enters the first room with this key there are unexpected rooms beyond, but it is always the master key that unlocks each door. John Hasbrouck van Vleck
The master key of knowledge is, indeed, a persistent and frequent questioning. Peter Abelard
Spirituality is the master key of the Indian mind. Sri Aurobindo