(noun) Something used for fastening, which can only be opened with a key or combination.
"Change is the key to unlocking growth."
"Technology is unlocking the innate compassion we have for our fellow human beings."
"There is no gate, no lock, no bolt that you can set upon the freedom of my mind."
"You might be locked in a world not of your own making, her eyes said, but you still have a claim on how it is shaped. You still have responsibilities."
"Lock up your libraries if you like; but there is no gate, no lock, no bolt that you can set upon the freedom of my mind."
"I thought how unpleasant it is to be locked out; and I thought how it is worse, perhaps, to be locked in."